Circadian rhythm

physical, mental, and behavioral changes that follow a 24-hour cycle.

Dreams

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

Electroencephalograph

1. the measurement of electrical activity in different parts of the brain and the recording of such activity as a visual trace (on paper or on an oscilloscope screen).

Hypersomnia

medical conditions in which you repeatedly feel excessively tired during the day (called excessive daytime sleepiness) or sleep longer than usual at night.

Insomnia

habitual sleeplessness; inability to sleep.

Melatonin

a hormone that your brain produces in response to darkness.

Napping

sleep lightly or briefly, especially during the day.

Narcolepsy

1. a condition characterized by an extreme tendency to fall asleep whenever in relaxing surroundings.

Night Terrors

a sudden feeling of extreme fear that awakens a sleeping person, usually during slow-wave sleep, and is not associated with a dream or nightmar

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 neurological disorder that causes unpleasant or uncomfortable sensations in your legs and an irresistible urge to move them.

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 common condition in which your breathing stops and restarts many times while you sleep.

Sleep deprivation

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

Sleep paralysis

a temporary inability to move or speak that occurs directly after falling asleep or waking up

Sleep study

a test that measures and records different body functions while you sleep.

Snoring

the action or fact of making a snorting or grunting sound while asleep.

Stage 1 (Non-REM) sleep

the first sleep stage you enter when nodding off.

Stage 2 (Non-REM) sleep

a continued slowing of heartbeat, breathing, muscle activity, and eye movements.

Stage 3 (Non-REM) sleep

deep sleep

Stage 4 (REM Sleep)

Rapid eye movement

Somnambulism

Somnambulism

Wakefulness

a condition of being alert, rather than sleepy