Advanced Sleep Phase Syndrome (ASPS) – a circadian rhythm disorder in which sleep onset occurs in early evening and as a consequence, wakefulness occurs in early morning. This disorder is more common in the elderly.

alpha waves – EEG (brain) wave activity that occurs during quiet wakefulness, such as when the eyes are closed. The frequency of alpha waves is between 8 to 12 hertz (cycles per second). It is indicative of the wakeful state in humans.

alternative medicine – any of the various practices or healing methods for treating illness that are not taught in a traditional curricula of a U.S. or U.K. medical school. Some of these include homeopathy, herbal remedies, acupuncture, meditation, chiropractic medicine, and faith healing.

anticonvulsant – a class of drugs that work to suppress sensory disturbances; they are often used to treat epileptic seizures.

antidepressant - a type of drug traditionally used to relieve or prevent psychiatric disorders associated with depression, but also used in the treatment of cataplexy, hypnagogic hallucinations, and sleep paralysis.

antihistamine – a drug that inhibits histamine, a compound that mediates inflammation and produces allergic reactions; antihistamines are a common ingredient in over-the-counter sleeping pills because of their sedative effect.

anxiolytics – a drug that relieves anxiety.

apnea – derived from Greek translated as "want of breath;" episodes of non-respiration during sleep that last at least 10 seconds. See central, chronic, or mixed sleep apnea.

arousal - "Partial" arousal is an abrupt change from a "deep" stage of NREM sleep (stage 3-4) to a "lighter" one (stage 2 or 1). "Full" arousal means awakening. During an arousal, your muscle tone increases, your heart may beat faster and you may move.

augmentation – a result of prolonged use of dopaminergic agents in which symptoms (of Restless Legs Syndrome) are chased into the daytime sometimes necessitating daytime dosing.

automatic behavior - performing activities or tasks with little or no recollection of the event.

awakening - "Spontaneous" awakenings most often start while you are in REM sleep, although you may awaken from NREM sleep, as well. When you are awake, your brain waves are of the alpha or beta pattern (see brain wave rhythms), your muscle tone is high and you can move voluntarily.

bedtime - defined as the time when one attempts to fall asleep (as distinguished from the time one gets into bed).

beta waves – EEG (brain) wave activity with a frequency of 13 to 35 hertz (cycles per second) that is typically seen in active wakefulness and also associated with taking psychotropic drugs, in which the eyes blink repeatedly.

benzodiazepine - a class of central nervous system depressants; examples include Valium (diazepam), Klonopin (clonazepam), Restoril (temazepam), and Halcion (triazolam); useful for managing insomnia, Restless Legs Syndrome, Periodic Limb Movement Disorder, sleepwalking, and REM Behavior Disorder.

bilevel positive airway pressure – an air compressor that blows a higher pressure for inhaling and a lower pressure for exhaling. BiPAP is generally used for apnea patients who can not tolerate high constant air pressure with CPAP.

bimaxillary advancement – a surgical procedure in which the upper and lower jawbones and teeth are moved forward and held in place with titanium plates and screws so that soft tissue structures are pulled forward, creating more space for the tongue.

"biological clock" – the term used to describe an internal timing mechanism that exists in most living systems and is thought to be located in the suprachiasmatic nucleus. It is the current explanation by which various cyclical behaviors and physiological processes are regulated and synchronized with environmental events.

biological rhythm – a regular pattern or cycle of change in an organism related to a physical variable, such as heart rate, body temperature, sleep-wake cycle, and so on.

BiPAP – an acronym for Bilevel Positive Airway Pressure; an alternative therapy to CPAP for the treatment of obstructive sleep apnea that allows for choosing a separate respiratory and expiratory pressure.

Brain-Wave Rhythms - Patterns of electrical activity of the brain. They include:

cataplexy - a temporary decrease or complete loss of muscle control triggered by an emotional response that is often seen in narcoleptics. Also, a sudden, dramatic drop in muscle tone and loss of deep reflexes, which leads to muscle weakness or paralysis (an attack may cause a person to collapse). It is usually triggered by an emotional stimulus such as laughing or being startled, or by some sudden physical exertion. Cataplexy is a symptom of narcolepsy, a neurologic disorder that causes excessive sleepiness.

central nervous system – also called the CNS; the part of the nervous system that consists of the brain and the spinal cord, which are responsible for the coordination of all motor and mental activities.

central sleep apnea - episodes of non-respiration during sleep for 10 second or longer that is caused by the brain failing to signal the respiratory muscles to breathe.

chronic insomnia - regular sleeplessness that lasts for more than three weeks and is persistent without treatment.

chronobiology – the scientific study of biological rhythms and timing mechanisms, sleep-wake cycles, heart rate, hibernation cycles, and body temperature.

circadian - a cycle that lasts about 24 hours.

circadian rhythms - the process of biological variations over 24 hours, coordinated by the suprachiasmatic nuclei in the brain, which regulate body temperature, hormone secretions, and other physiological functions.

cognitive-behavioral therapy – psychological therapy which focuses on changing attitudes and beliefs related to sleep and insomnia.

complementary medicine – the science of combining one or more conventional treatments with one or more alternative treatments to aid in the healing process. For example, treatment for insomnia might include a medication in combination with relaxation therapy.

compulsive hyperphagia – a disorder of excessive and compulsive overeating; it is often accompanied with other disorders, such as hypersexuality and hypersomnia, and is also associated with Kleine-Levin syndrome.

continuous positive airway pressure - also called CPAP; a type of therapy used to effectively treat obstructive sleep apnea in which an air compressor forces air through the nose and into the airway by way of a light mask worn over the nose during sleep.

cortisol – (the same as hydrocortisone) a steroid hormone produced in the adrenal gland that influences the metabolism of various cell types.

CPAP – an acronym for Continuous Positive Airway Pressure; an effective therapy used to treat obstructive sleep apnea.

Delayed Sleep Phase Syndrome (DSPS) – a circadian rhythm sleep disorder characterized by difficulty achieving sleep onset in the evening and difficulty waking up at a desired time in the morning. It involves a desired sleep time out of sync with physiologic sleep time.

delta waves – EEG activity with a frequency of less than 4 hertz (cycles per second) that is most often seen in Stage 3 and 4 of non-REM sleep.

delta sleep – also called slow wave sleep; a term used to describe the stages of sleep characterized by delta waves. It is regarded as the most restorative time of sleep.

dopaminergic agents – a class of drugs synthesized with the neurotransmitter dopamine and is most often used to treat Parkinson’s patients; often helpful in managing Restless Legs Syndrome and Periodic Limb Movement Disorder.

dreams - periods of intense vivid imagery during sleep, often associated with rapid eye movements.

electroencephalogram - also called an EEG; the measurement and recording of brain wave activity. Frequency measurement in hertz ranges from below 3.5 per second (delta), 4 to 7.5 second (theta), 8 to 12 second (alpha), and above 13 second (beta). Electrodes are typically placed at C3 and C4 positions on the scalp.

electromyogram - also called an EMG; the measurement and recording of muscle activity, particularly under the chin, along the jaw, and on the legs.

electro-oculogram - also called an EOG; the detection and recording of eye movements, essential for determining the different sleep stages.

endogenous circadian pacemaker – an internal mechanism in the brain, thought to be at the site of the suprachiasmatic nucleus, that drives periodic processes, such as the sleep-wake cycle, body temperature, and cortisol release, in the human circadian timing system.

enuresis – also called bed-wetting or sleep enuresis; uncontrolled urination during sleep. This disorder is more common in children and often related to maturation; however, repeated nocturnal bed-wetting can indicate other physical or emotional problems. 

excessive daytime sleepiness – sometimes called excessive sleepiness, the inability to stay awake during the normal wake period of a sleep-wake cycle or may involve involuntary sleep. Common causes include: insufficient sleep, sleep apnea, narcolepsy, and insomnia.

"Factor S" – a substance in the cerebrospinal fluid that has sleep-inducing properties.

fragmentation - the interruption of any stage of sleep due to appearance of another stage or waking. Sleep fragmentation connotes repetitive interruptions of sleep by arousals and awakenings.

genioglossus muscle - a muscle that attaches from the back of the tongue to a region on the back of the chin and serves to advance, retract and depress the tongue.

genioglossus advancement – a surgical operation that detaches the genioglossus muscle from its insertion point and reattaches it in a more advanced position in order to pull the back of the tongue forward, enlarging the air space behind the tongue.

glossectomy - the surgical reduction or removal of the tongue, used to open the lower airway or to remove cancerous tissue.

Hertz (Hz) – the unit of measurement for cycles per second; used to measure EEGs.

homeostatic - (homeostasis, n.) the balanced state of the living body (i.e. temperature, chemistry, blood pressure, sleep and wakefulness, and so on), despite variations in the environment.

hyoid advancement – a surgical operation in which the hyoid bone is moved forward and either attached to the Adam's apple or to the jawbone, enlarging the air space behind the tongue.

hyoid bone – a C-shaped bone in the upper neck positioned above the Adam's apple with muscle attachments to the back of the tongue, as well as the sides of the lower throat.

hypersomnia – also called excessive (daytime) sleepiness or somnolence; the inability to remain awake during an individual’s normal wake period.

hypnagogic hallucinations – vivid, often frightening, dream-like images and sounds experienced at REM sleep onset, usually accompanied by fear and anxiety; a characteristic feature of narcolepsy.

hypnic jerk – also called sleep starts; the sensation of falling and then a physical jerk into wakefulness, usually during Stage 1 sleep. 

hypnotic - also called a sleeping pill, sedative, or a sedative-hypnotic medication; a medication that causes drowsiness, induces sleep onset, and/or maintains sleep.

"hypnotoxin" – also called sleep promoting substance (SPS); the term coined by Henri Pieron in 1907 that described a sleep-inducing substance thought to be in the cerebrospinal fluid.

hypopnea – an episode of abnormally slow or shallow respiration during sleep that lasts longer than 10 seconds. Hypopnea differs from apnea in that some airflow is present.

hypothalamus – the region at the base of the brain involved in autonomic processes such as temperature regulation, food intake, and emotional activity, and thought to be important in the role of sleep and wakefulness.

idiopathic – occurring spontaneously and without known cause.

idiopathic hypersomnia – a disorder of excessive sleepiness in which the affected individual sleeps longer than normal (greater than 10 hours), is excessively sleepy, falls asleep at inappropriate times, and frequently takes naps. Its exact cause is unknown.

insomnia – the inability to sleep applied to the general complaint of having trouble falling or staying asleep; insomnia is a symptom usually caused by underlying problems. See also transient, short-term, chronic, and sleep onset insomnia.

jet lag - a condition that occurs following air travel through multiple time zones (usually 3 of more zones) and is characterized by various psychological and physiological effects, such as fatigue, gastrointestinal disturbances, and irritability, caused by a disruption in circadian rhythms.

K-complex – high voltage EEG activity that consists of a sharp upward component followed by a slower downward component and lasts more than .5 seconds; required for definition of Stage 2 non-REM sleep.

Kleine-Levin syndrome – a disorder distinguished by recurrent hypersomnia, compulsive overeating, and hypersexuality and first described by Willi Kleine in 1925 and then by Max Levin in 1929.

lark – also called a morning person or morning lark; a person who prefers go to bed early in the evening and rise early in the morning. This tendency becomes more common in the elderly.

laser-assisted uvulopalatoplasty (LAUP) - a surgical procedure for the treatment of habitual loud snoring or obstructive sleep apnea that involves removal of the back edge of the palate, the uvula, and if present, the tonsils.

latency period - an interval. Sleep latency is the interval from "lights out" until sleep begins. REM latency is the period from the beginning of sleep to the first appearance of rapid eye movement (REM) sleep.

L-Dopa – also called dopaminergic agents; a dopamine-enhancing class of drugs most often used to treat Parkinson’s patients; often helpful in managing Restless Legs Syndrome and Periodic Limb Movement Disorder. Examples include L-Dopa with Sinemet (carbidopa), Permax (pergolide), and Parlodel (bromocriptine).

"leucomaines" – the name for the poisonous substances that supposedly accumulated during the day and passed from the blood to the brain. Leo Errera proposed that these substances in the 1880s were the cause of sleep.

light box – a commercially available, electrically-powered instrument that provides artificial light; a treatment option for patients with Seasonal Affective Disorder, Advanced Phase Sleep Disorder, or Delayed Phase Sleep Disorder.

light therapy – a treatment for various disorders including seasonal affective disorder, depression, hypersomnia, and delayed phase sleep disorder. It involves properly timed exposure to bright light to promote a normal sleep-wake cycle and decrease sleep disturbances.

lingualplasty – a surgical procedure that involves a resection of the tongue with additional removal of side wedges in order to reduce the back of the tongue and open the lower airway.

lingual tonsils - tonsil-like tissue on the back part of the tongue.

lux – a measure of light intensity; the unit used by light box manufacturers to describe light output.

maintenance of wakefulness test – also called MWT, a test that consists of four 20-minute trials conducted every 2 hours and is used to determine a patient’s ability to stay awake during the day. Contrary to a MLST, the MWT is scored on the patient’s ability to remain awake during the trials.

melatonin – in nature, a hormone that is secreted by the pineal gland in the brain in response to darkness, and has been linked to regulation of circadian rhythms; a derivative of melatonin marketed as a health food supplement is commercially available.

mental imagery – the process of creating images in the mind.

microsleep - a lapse from wakefulness into sleep that lasts just a few seconds.

mixed sleep apnea - the combination of central and obstructive sleep apnea.

montage – the term applied to the testing variables and their order on polysomnogram paper or a computer monitor, such EEG, EOG, heart rate, and so on.

MSLT – the acronym for multiple sleep latency test; a test used to study and document excessive daytime sleepiness by way of a series of naps at two-hour intervals.

multiple sleep latency test - a test used to study and document excessive daytime sleepiness by way of a series of naps at two-hour intervals.

MWT – an acronym for the maintenance of wakefulness test, in which four 20-minute trials are conducted every two hours and the patient is encouraged to stay awake.

myoclonus - see nocturnal myoclonus.

narcolepsy - a physical condition characterized by episodes of inappropriate and often involuntary sleep in the form of naps that may last a few minutes to hours; usually accompanied by cataplexy, sleep paralysis, and hypnagogic hallucinations.

National Sleep Foundation (NSF) – established in 1990 as an "independent nonprofit organization dedicated to improving public health and safety by achieving public understanding of sleep and sleep disorders."

negative sleep conditioning - a psychological state perpetuated by self-induced stress and anxiety of needing to attain sleep; specifically, it refers to an inability to sleep at night in one’s own bed.

neuron – a type of nerve cell (or brain cell) that has a central cell body (axon) and long endings (dendrites) specialized to receive, conduct, and transmit signals in the nervous system.

nightmare - a sleep-disrupting dream that is often recalled in detail. An anxiety-filled dream that often wakes the sleeper from REM sleep. It is distinguished from "sleep terror," which is sudden, partial arousal from NREM sleep that may cause the sleeper to cry out in fright but that seldom includes vivid images.

night owl – also called a night person or evening person; a name applied to someone who prefers to stay up into the night or early morning and arise in late morning.

nocturia – also called nycturia; frequent urination at night that results in arousal of sleep and rising frequently to go to the bathroom. It can be caused by urological problems, infection, a tumor, or medication and has been associated with the development of obstructive sleep apnea.

nocturnal – of the night or night-related; the opposite of diurnal.

nocturnal myoclonus - a brief rapid twitch that occurs at night as a result of a sudden contraction of one or more muscle groups; former name of Periodic Limb Movement Disorder.

non-REM sleep - a state of sleep characterized by four stages that range from light dozing to deep sleep; 75% of sleep is spent in non-REM sleep. In stages 3 and 4 of NREM sleep, there is a decrease in blood pressure, muscle activity, and respiratory rate as the sleeper relaxes.

normal hypersomnia – a disorder in which the affected individual requires more sleep than normal, i.e. more than 10 hours of sleep per day, and which may be the result of a genetic predisposition. Normal hypersomniacs are also called "naturally long sleepers."

obstructive sleep apnea (syndrome) - also called OSA; a common form of apnea, in which the airway is blocked, resulting in a lack of respiration and a momentary interruption of sleep; usually caused by physical abnormality.

opiate - a class of codeine-derived, controlled narcotics, such as Tylenol #3, Percocet (oxycodone), Darvon (propoxyphene) and methadone; used to manage severe cases of Restless Legs Syndrome and Periodic Limb Movement Disorder.

OTCs – an acronym for over-the-counter medications, those that are available for purchase without a prescription.

OSA – an acronym for obstructive sleep apnea; a common form of apnea

otolaryngology – the medical study of the ears, nose, and throat (ENT)

over-the-counter medications – drugs that available to the general public without a prescription.

paradoxical therapy - an effective therapeutic approach to conquering insomnia that asks the insomniac to do the exact opposite of trying to fall asleep.

parasomnia - a term used to describe uncommon disruptive sleep-related disorders, such as sleepwalking, sleep talking, and nightmares.

pavor nocturnus – a term derived from Latin pavor, terror, and nocturnus, at night. See also sleep terrors.

Periodic Limb Movement Disorder - also called PLMD, Periodic Limb Movement Syndrome, or PLMS; a condition in which the legs or arms twitch or move involuntarily and periodically during sleep.

periodic limb movement index - the record of the number of leg or arm movements during each hour of sleep measured by sensors placed on the legs and arms.

Pickwickian syndrome – the first term applied to obstructive sleep apnea, originally described by Charles Dickens in 1836. It referred to people who were excessively sleepy, loud snorers, and overweight.

PLMD – an acronym for Periodic Limb Movement Disorder; a condition in which the legs or arms twitch or move involuntarily and periodically during sleep.

polyp – a projecting growth or mass, usually benign, that forms in a mucous membrane and in the nasal passages, causes obstructed airflow.

polysomnogram - also called a PSG, sleep study, or sleep test; a non-invasive test that records vital signs and physiology during a night of sleep. It includes measurements from an EEG, EMG, and EOG, as well as respiratory airflow, blood oxygen saturation, pulse rate, heart rate, body position, and respiratory effort.

postprandial dip - a slight drowsiness caused by a natural drop in body temperature, particularly in early afternoon and after a meal.

post-traumatic hypersomnia – a disorder of excessive sleepiness that appears within 18 months of a traumatic event involving a central nervous system-related accident.

primary snoring - snoring not associated with apnea. 

Process C – the natural behavior and tendency, regulated by human circadian rhythms, to sleep during the "sleepy phase" of the body, usually between 11:00 p.m. and 7:00 a.m.

Process S – also known as the homeostatic process, it is the disposition of a normal person who is sleep-deprived to become sleepy when awake, and sleep deeper and longer when sleep is achieved.

pupillometry – the measurement of pupil diameter and activity as related to alertness or sleepiness. This test is used more for research rather than a diagnostic assessment.

radio-frequency tissue ablation – a technique that uses radio-frequency waves via a needle electrode placed under the surface of the tissue, resulting in contraction and subsequent shrinkage of excessive tissues that cause snoring.

recurrent hypersomnia – a disorder of excessive sleepiness that occurs weeks or months apart, often accompanied with other disorders such as hypersexuality or compulsive eating.

relaxation therapy – also termed relaxation imagery; various methods or techniques for the alleviation of insomnia that help to relax the mind and the body and which can facilitate sleep onset.

REM latency - the period of time in the sleep period from sleep onset to the first appearance of REM sleep. 

REM onset - the designation for commencement of a REM period.

REM percent - the proportion of total sleep time constituted by the REM stage of sleep.

REM Rebound or Recovery - an increased amount of REM sleep for a few nights after a period of REM deprivation. REM rebound may occur after several days without sleep, or upon withdrawal from certain drugs, including some sleeping pills, that suppress REM sleep. Increased amounts of REM sleep may be reflected by disturbing dreams.

REM sleep - also known as "paradoxical" sleep, this state of sleep is characterized by rapid eye movement (REM), muscle paralysis, and irregular breathing, heart rate, and blood pressure. Dreaming takes place during REM sleep.

respiratory disturbance index (RDI) - a record of the number and duration of apnea episodes, both obstructive and central, during each hour of sleep. An RDI of greater than 5 is regarded as abnormal.

Restless Legs Syndrome - also called RLS; a neurological disorder of unknown cause that causes irrepressible twitching and creeping sensations in the legs while sitting or lying down.

RLS – an acronym for Restless Legs Syndrome; a disorder that causes irrepressible and uncontrollable tingling sensations in the legs.

SAD – an acronym for seasonal affective disorder; a disorder with depression-like symptoms that occurs in the late fall because of less light exposure and diminishes with the onset of spring.

SCN – an acronym for suprachiasmatic nuclei and sometimes called the endogenous circadian pacemaker; small structures in the brain, sensitive to the presence or absence of light, that coordinate circadian rhythms.

seasonal affective disorder – a disorder characterized by depression, sleeping too much, overeating, diminished sex drive, working less productively, and other depression-related symptoms that occurs in the mid-to-late fall due to less light exposure. Symptoms usually diminish with the onset of spring.

sedative – also called a sleeping pill or hypnotic; a medication that causes drowsiness, induces sleep onset, and/or maintains sleep.

selective serotonin reuptake inhibitors - a class of antidepressants that assist nerve impulses along pathways using the neurotransmitter serotonin; effective in treating narcolepsy symptoms. Examples include: Zoloft, Prozac, and Paxil.

septoplasty – a surgery sometimes used to treat obstructive sleep apnea in which a small incision is made inside a nostril, and the cartilage and bone of the septum is straightened.

septum – the divider between the two nasal passages; if deviated (crooked), the septum can obstruct the nasal passages.

serotonin – a neurotransmitter found in brain stem cells and other parts of the central nervous system; in animal studies, the inhibition of the formation of serotonin led to severe insomnia.

short-term insomnia - temporary sleeplessness that arises because of ongoing stress, a temporary illness, or a traumatic experience.

sleep - a physical and mental resting state in which a person becomes relatively inactive and unaware of his or her environment.

sleep apnea - episodes of non-respiration during sleep that last at least 10 seconds and occur 5 times per hour of sleep; see central, chronic, or mixed sleep apnea.

sleep architecture – the structure of the sleep cycle and wakefulness as it occurs over a period of sleep.

"sleep center" – a localized area in the brain believed to regulate sleep.

sleep cycle - the cycle in which non-REM and REM sleep alternate in 90- to 110- minute phases. A normal sleep pattern has 4 to 5 sleep cycles.

sleep debt - the deficiency of sleep created when personal sleep requirements are not met.

sleep deprivation - a mental and physical state that arises when sleep has not been attained or has been inhibited. In some cases, it can cause an inability to concentrate, loss of memory, and rarely, hallucinations and erratic behavior.

sleep disorders - physical and psychological conditions or disturbances of sleep and wakefulness, usually caused by abnormalities that occur during sleep or by abnormalities of specific sleep mechanisms.

sleep efficiency - the proportion of sleep in the period potentially filled by sleep; that is, the ratio of total sleep time in bed.

sleep hygiene - the practice of achieving and maintaining proper habits to promote good sleep.

sleep latency - the period of time measured from "lights out," or bedtime, to the commencement of sleep.

sleep maintenance insomnia – one or more episodes of wakefulness that occur later in the night and may be due to medical illness, primary sleep disorders, or depression. 

sleep medicine - the science of the study of sleep and its processes; also refers to the clinical practice of assessing and treating sleep disorders.

sleep mentation - the imagery and thinking (and emotion) experienced during sleep.

sleep onset - the transition from the awake to the sleep state, normally into NREM stage 1 (but in certain conditions, such as infancy and narcolepsy, into REM.) Most polysomnographers accept EEG slowing, reduction and eventual disappearance of alpha activity, presence of EEG vertex spikes and slow rolling eye movements (the components of NREM stage 1) as sufficient for sleep onset; others require appearance of stage 2 wave forms. (See sleep latency, sleep stages.)

sleep onset insomnia - insomnia characterized by a delay in falling asleep, lasting 30 minutes or longer, at the time when one goes to bed; it is most commonly caused by anxiety.

sleep paralysis - a brief loss of muscle control that occurs at the onset of sleep or upon awakening; a condition usually associated with narcolepsy. May last from a few seconds to a few minutes. Occurs in one in twenty healthy people but is more common in those with narcolepsy. 

sleep restriction therapy – a behavioral treatment developed by Dr. Arthur Spielman and colleagues that follows a simple principle: Restrict time in bed to only the number of hours asleep, then increase time in bed as sleep efficiency increases.

sleep spindles – a pattern of EEG waves that consist of a burst of 11 to 15 hertz waves that last for .5 to 1.5 seconds; an identifying feature of Stage 2 sleep.

sleep talking - also called somniloquy; a parasomnia characterized by talking during sleep.

sleep terrors - also called pavor nocturnus or night terrors; a parasomnia characterized by episodes of screaming or shouting and occasionally, sleepwalking. Sleep terrors are usually associated with fear and anxiety.

sleep-wake cycle – the repeated pattern over 24 hours that consist of periods of sleep alternating with periods of wakefulness.

sleepwalking - also called somnambulism; a parasomnia characterized by walking or performing other complicated activities while asleep.

Slow Wave Sleep (SWS) - synonymous with sleep stages 3 and 4.

snoring - the noise produced by a sleeping individual in which the soft palate and the uvula vibrate during respiration.

somnambulism - see also sleepwalking; a parasomnia characterized by walking or performing other complicated activities while asleep.

somniloquy - (somniloquism) see also sleep talking; a parasomnia characterized by talking during sleep.

somnolence – also called excessive sleepiness or excessive daytime sleepiness; the inability to stay awake during the normal wake period of a sleep-wake cycle. It can be measured by a multiple sleep latency test (MSLT)

somnologist - a specialist in the study of sleep and in the diagnosis and treatment of sleep disorders.

somnoplasty – a non-invasive procedure that uses radio frequency to reduce structures in the mouth in the treatment of snoring and obstructive sleep apnea.

Stage 1 sleep - the brief, dozing stage of non-REM sleep in which a person transitions to very light sleep and can be awakened easily, characterized by low voltage EEG and slow rolling eye movements; 5% of non-REM sleep is spent in Stage 1.

Stage 2 sleep - the stage of consolidated sleep in non-REM sleep characterized by sleep spindles and K-complexes; 45% of non-REM sleep is spent in Stage 2.

Stage 3 sleep - the stage of deeper sleep in non-REM sleep characterized by delta waves interspersed with smaller, faster waves; 12% of non-REM sleep is spent in Stage 3.

Stage 4 sleep - the stage of very deep sleep in non-REM sleep almost exclusively composed of delta waves and the stage in which sleep terrors or sleepwalking may occur; 13% of non-REM sleep is spent in Stage 4.

stimulant - a type of drug, such as Cylert, Ritatlin, and Dexedrine, that stimulates the central nervous system; often used to treat excessive daytime sleepiness.

stimulus control – an effective insomnia technique developed by Dr. Richard Bootzin and colleagues which proposes that an individual has 10 minutes to fall asleep. If sleep is not achieved, the person must get up, go into another room, and return to bed only when sleepy. Also called the 10-minute rule.

suprachiasmatic nuclei - also called the SCN or the endogenous circadian pacemaker; small structures in the brain, sensitive to the presence or absence of light, that coordinate circadian rhythms.

teethgrinding - also called bruxism; a parasomnia characterized by the grinding or clenching of teeth during sleep.

The 10-Minute Rule – a relaxation and sleeping technique that suggests that an individual who has laid awake in bed for an estimated 10 minutes to get up, go into another room, relax by doing something boring, and then return to bed when sleepy.

tonsils – masses of lymphoid tissue at the back of both sides of the mouth whose primary function is fighting infection.

tonsillectomy - surgical removal of the tonsils.

total sleep period - the period of time measured from sleep onset to final wakening. In addition to total sleep time, it is comprised of the time taken up by arousals and movement time until wake-up. (See Sleep Efficiency).

total sleep time - the amount of actual sleep time in a sleep period; equal to total sleep period less movements and awake time. Total sleep time is the total of all REM and NREM sleep in a sleep period.

tracheostomy – also known as a tracheotomy; a surgical procedure that creates an opening in the windpipe via the neck in order to insert a tube that facilitates breathing. This procedure is reserved for patients with severe sleep apnea.

transient insomnia – sometimes called adjustment sleep disorder or situational insomnia, it is sleeplessness that lasts a few consecutive nights and is often triggered by stress or excitement.

turbinate – also called the nasal concha; any of three bones (lowest, middle, and upper) within the nose that are surrounded by soft tissue and form the sides of the nasal cavity.

turbinate reduction – a surgical procedure used to reduce the size of an enlarged turbinate, which can improve the size of the nasal airway, thereby relieving obstructive sleep apnea.

UPPP – an acronym for uvulopalatopharyngoplasty; the surgical procedure for the removal of the uvula and tightening of loose tissue in the back of the throat.

"urotoxins" – coined by Abel Bouchard in 1886, a term he used to describe toxic agents excreted in the urine during sleep.

uvula - the tissue that hangs down in the back of the throat.

uvulopalatopharyngoplasty - also called UPPP; the surgical procedure for the removal of the uvula and tightening of loose tissue in the back of the throat.

vigilance testing – the process of assessing the level of alertness during wakefulness in a clinical or research setting. It may include a series of tests such as the Epworth Sleepiness scale, pupillometry, reaction time tests, a MLST, or MWT.

wakefulness – a brain state that occurs when a healthy individual is not asleep.