Abdominal Movement - In diagnostic sleep studies, abdominal movement is recorded. This is one of the measures of respiratory effort, reflecting movement of the diaphragm.

Advanced Sleep Phase Syndrome (ASPS) - Phases of the daily sleep/wake cycle are advanced with respect to clock time.  This is classified as a circadian rhythm disorder.   The sleep phase occurs well ahead of the conventional bedtime and the tendency is to wake up too early.

Alpha rhythm - EEG oscillations, prominent over the occipital cortex, with a frequency of 8-13 Hz in adults;  indicative of the awake state; present in most, but not all, normal individuals;  most consistent and predominant during relaxed wakefulness.

Ambulatory Monitor - Portable system used to continuously record multiple physiological variables during sleep.

Antihistamine - A type of chemical present in many cold and allergy medicines, and some nonprescription sleep medicines. When taken at night as sleep aids, antihistamine-containing medicines may result in daytime drowsiness.

Apnea - Literally means "no breath";  the cessation of airflow at the nostrils and mouth for at least 10 seconds.

Apnea/Hypopnea Index (AHI) - The number of apneas and hypopneas (abnormally slow breathing) per hour. 5-20=mild, 21-50=moderate, above 51 is considered to be severe.

Arousal - Abrupt change from sleep to wakefulness, or from a "deeper" stage of non-REM sleep to a "lighter" stage

Arousal Disorder - Parasomnia disorder presumed to be due to an abnormal arousal function.  Classical arousal disorders:  sleepwalking, sleep terrors and confusional arousals.

Barbiturates - Sedating medications that were used as sleep aids years ago but are rarely prescribed for insomnia today, due to their overall safety risks.

Benzodiazepines - A class of medications often prescribed for sleep problems. This class includes both long-acting medicines (which can linger in the body and potentially cause daytime drowsiness) and short-acting medicines (which do not stay in the bloodstream as long). Many benzodiazepines were originally formulated to treat anxiety. See Non-benzodiazepines.

Bruxism - See Teeth grinding.

Insomnia - Sleep problems characterized by difficulty falling asleep, frequent awakenings during the night, or waking up earlier than desired. Insomnia can result in getting up in the morning feeling un-rested and experiencing drowsiness during the day.

Jet Lag - Condition resulting when travel across time zones leaves a person feeling “out of sync” with local time at his or her destination.

Melatonin - A naturally occurring hormone associated with sleep. Synthetic forms of melatonin are sold as sleep aids, although clinical data supporting melatonin use are insufficient.

Microsleeps - Fleeting, uncontrollable episodes of sleep occurring when one is awake. Although they may last only a few seconds, micro-sleeps can cause car accidents, machinery-related accidents, and other dangerous conditions.

Narcolepsy - A sleep disorder marked by sudden, uncontrollable urges to sleep, causing an individual to fall asleep at inappropriate times. Medications and behavioral approaches such as scheduled naps can help control narcolepsy.

Nightmare - A frightening dream that can cause an individual to wake up. Nightmares typically occur during REM sleep.

Non-benzodiazepines - A class of sleep medicines. Currently available medicines in this group typically do not lead to daytime drowsiness.

NREM Sleep — Non-rapid eye movement sleep. A stage of sleep in which brain activity and bodily functions slow down. NREM sleep accounts for the largest portion of the sleep cycle.

Progressive Relaxation - A technique that involves relaxing the body’s muscle groups in a progressive sequence, usually starting at the toes and moving upward toward the head.

REM Sleep - Rapid eye movement sleep. REM sleep occurs in brief spurts of increased activity in the brain and body. REM is considered the dreaming stage of sleep. It is characterized by the darting of the eyes under the eyelids.

Sleep Apnea - A condition characterized by temporary breathing interruptions during sleep. The pauses in breathing can occur dozens or even hundreds of times a night. Symptoms include loud snoring and a gasping or snorting sound when the sleeping individual starts to breathe again. Although the individual may not be aware of having sleep apnea, the condition can disrupt the quality of sleep and result in daytime fatigue. The most common type, obstructive sleep apnea, occurs when the tongue or other soft tissue blocks the airway. Treatments include breathing devices that keep the airway open during sleep, and surgery that reduces the amount of soft tissue near the airway.

Sleep Center - A laboratory or other clinical facility equipped to diagnose sleep disorders.

Sleep Cycle - A sequence of sleep stages that usually begins with a period of about 80 minutes of NREM sleep followed by about 10 minutes of REM sleep. This cycle of approximately 90 minutes is repeated four to six times each night. If the sequence is interrupted (for example, by external noise or a sleep disorder), the quality of sleep can suffer.

Snoring - Hoarse, often loud breathing sound that occurs during sleep. Snoring often occurs when the soft palate in the mouth vibrates. Snoring may be a sign of sleep apnea.

Teeth Grinding (bruxism) - Occurring during sleep, teeth grinding can disrupt sleep and lead to daytime fatigue. It can also damage teeth, gums, and jaw bones. To help prevent damage, dentists often recommend using a plastic mouth guard.

Thermoregulation - Regulation of body temperature in mammals.