Circadian rhythm

hysical, mental, and behavioral changes an organism experiences over a 24-hour cycle.

Dreams

a series of thoughts, images, and sensations occurring in a person's mind during sleep.

Electroencephalograph (EEG)

a test that measures electrical activity in the brain using small, metal discs

Hypersomnia

the inability to stay awake and alert during the day despite having more than an adequate amount of nighttime sleep.

Insomnia

habitual sleeplessness; inability to sleep.

Melatonin

a hormone secreted by the pineal gland that inhibits melanin formation and is thought to be concerned with regulating the reproductive cycle.

Napping

A nap is a short period of sleep

Narcolepsy

a sleep disorder that makes people very drowsy during the day.

Night Terrors

feelings of great fear experienced on suddenly waking in the night

Nightmares

a frightening or unpleasant dream.

Parasomnia

any of a group of sleep disorders characterized by the regular occurrence of abnormal movements, vocalizations, or experiences, such as sleepwalking, talking in one's sleep, or night terrors.

Restless Legs Syndrome

a disorder characterized by the occurrence of uncomfortable sensations in the legs and the urge to move them in order to relieve the sensations, typically occurring in the evening or at night and often interfering with sleep.

Sleep

a condition of body and mind that typically recurs for several hours every night, in which the eyes are closed, the postural muscles relaxed, the activity of the brain altered, and consciousness of the surroundings practically suspended.

Sleep apnea

a potentially serious sleep disorder in which breathing repeatedly stops and starts.

Sleep deprivation

the situation or condition of suffering from a lack of sleep.

Sleep paralysis

a feeling of being conscious but unable to move.

Sleep study

test used to diagnose sleep disorders.

Snoring

a test used to diagnose sleep disorders.

Stage 1 (Non-REM) sleep

the first sleep stage you enter when nodding off.

Stage 2 (Non-REM) sleep

still light sleep, but deeper than stage 1.

Stage 3 (Non-REM) sleep

deep sleep

Stage 4 (REM Sleep)

an even deeper sleep where the brain waves further slow and sleepers are very difficult to wake.

Somnambulism

sleepwalking.

Wakefulness

not sleeping or able to sleep : sleepless.