Circadian rhythm

the 24-hour internal clock in our brain that regulates cycles of alertness and sleepiness by responding to light changes in our environment.

Dreams

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

Electroencephalograph (EEG)

a recording of brain activity

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 which inhibits melanin formation and is thought to be concerned with regulating the reproductive cycle.

Napping

sleep lightly or briefly, especially during the day.

Narcolepsy

Excessive daytime sleepiness. People with narcolepsy fall asleep without warning. It can happen anywhere and at any time

Night Terrors

feelings of great fear experienced on suddenly waking in the night.

Nightmares

a frightening or unpleasant dream.

Parasomnia

An abnormal disruption of sleep, such as sleep walking, sleep talking, nightmares, bedwetting, sleep apnea (problems with breathing that cause loud snoring), or nighttime seizures

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

a test used to diagnose sleep disorders

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

a period of deep sleep where any environmental noises or activity may fail to wake the sleeping person

Stage 4 (REM Sleep)

the stage of sleep where most dreams happen

Somnambulism

sleepwalking.

Wakefulness

not sleeping or able to sleep : sleepless.