Descriptionary

arousal disorder term referring to either sleepwalk­ing or night terrors.

biological clock a physiological cell mechanism that regulates one's sleep-wake cycles.

brain waves the brain's electrical activity, which changes through the various cycles of sleep.

bruxism teeth-grinding during sleep.

chronotherapy the therapeutic use of light to change sleep-wake patterns.

circadian referring to a period of 24 hours.

circadian rhythm any 24-hour cycle within the body's regulatory system, and especially the sleep- wake cycle.

conditioned insomnia a form of insomnia in which the sufferer is so afraid of his inability to fall asleep that he cannot relax enough to drift off and thus ful­fills his own fear. Also known as learned insomnia.

CPAP machine continuous positive airway pres­sure machine. In patients who suffer from obstruc­tive sleep apnea, a device that blows air through a mask and into the nasal passages in order to keep the airway open during sleep, thus preventing breathing cessation and disturbed sleep.

delayed sleep phase syndrome a natural sleep cycle that has become out of sync with the sleeper's desired bedtime, causing drowsiness later than normal.

delta sleep stages 3 and 4 sleep, the deepest phase of sleep, when the brain produces mostly delta waves and its electrical activity slows dramatically.

drowsiness a strong feeling of sleepiness, marked by droopy or heavy eyelids.

electroencephalogram a measurement of the brain's electrical activity. Also called an EEG.

entrain to train one's behavior to align with the body's natural cycles, for example, to avoid going to bed until one feels drowsy.

enuresis bed-wetting.

GABA gamma-aminobutyric acid. In the brain, a neurotransmitter involved in sedation, muscle relax­ation, and sleep.

homicidal sleepwalking related to sleepwalking, killing or attempting to kill someone during sleep.

hypersomnia excessive sleep.

hypnagogia that which occurs between the state of sleep and wakefulness, including hallucinations, out- of-body experiences, geometrical or other meaning­less imagery behind the eyes, etc.

hypnagogic of the mental state that occurs just before one falls asleep or after one begins to wake.

hypnagogic hallucination unrelated to REM or dream sleep, a hallucination that occurs just as one is falling into or out of sleep and is considered normal.

hypnic jerk caused by a normal electrical distur­bance as one falls asleep, a sudden muscle jerking in a leg, arm, or jaw, as if one has been startled.

Hypnos in Greek mythology, the personification of sleep.

hypnotics a class of drugs that facilitate sleep.

insomnia trouble falling or staying asleep.

jet lag the temporary fatigue and insomnia travelers suffer when staying in a different time zone, due to a shift in their natural sleep-wake cycle.

Klein-Levin syndrome a disorder characterized by excessive sleep, up to 20 hours at a time, and uninhib­ited sexual behavior.

light sleep stage 1 or stage 2 sleep, characterized by a lack of dreaming, from which sleepers may be easily awakened.

light therapy the use of very bright light to set or reset one's biological clock. It is also used to help regulate moods, especially in cases of seasonal affec­tive disorder.

lucid dreaming any dream state in which the dreamer is aware that he is dreaming and can con­trol part of its contents. Also known as conscious dreaming.

melatonin a sleep-regulating hormone secreted by the pineal gland.

micro-arousal a partial or brief awakening from sleep, usually not remembered by the sleeper.

micro-sleep a brief dozing, usually lasting no more than a few seconds, which may occur several times a day in people who are chronically sleep-deprived.

Morpheus in Greek mythology, the god of dreams.

narcolepsy a sleep disorder in which sufferers expe­rience excessive daytime sleepiness and may some­times fall uncontrollably into deep sleep at any time.

natural short sleeper one who sleeps one to three hours less than average but feels fully refreshed dur­ing the day.

nightmare a frightening or horrifying dream that occurs during REM sleep and may awaken the sleeper.

night terrors suffered by some young children, a vivid hallucination occurring during a partial awak­ening from deep sleep, accompanied by panic and often crying. Unlike nightmares, night terrors do not occur during dream or REM sleep and are usually not remembered.

nocturnal referring to the night or occurring at night.