Sleep

Definition

Sleep is a naturally recurring state of mind and body characterized by altered consciousness, relatively inhibited sensory activity, reduced muscle activity and inhibition of nearly all voluntary muscles.

Related terms

REM Sleep: Rapid Eye Movement (REM) sleep is a stage of sleep characterized by quick random movements of eyes, dreaming and bodily movement. It's when most vivid dreams occur.

Non-REM Sleep: This is the part of sleep that consists of stages 1-3. It ranges from light dozing off (stage 1) to deep restorative sleep (stage 3).

Insomnia: A common sleep disorder that can make it hard to fall asleep or stay asleep or cause you to wake up too early and not be able to get back to sleep.