Sleeps

Sleeps is the present-tense, third-person singular form of the verb sleep. Sleep, in general, is a natural, periodic state of rest for the mind and body, during which consciousness is altered, sensory activity is reduced, and voluntary muscles are inhibited. Sleep is essential for health and performance, though its exact functions are still studied.

In humans, sleep occurs in cycles that include non-rapid eye movement (NREM) and rapid eye movement (REM) sleep. NREM sleep has progressively deeper stages; REM sleep features brain activity similar to wakefulness and dreaming. A typical adult experiences about four to six cycles per night, totaling seven to nine hours, though requirements vary.

Regulation and functions: The circadian system, governed by the hypothalamus, aligns sleep with day-night cycles; homeostatic sleep pressure increases with time awake. Sleep supports learning and memory, metabolic regulation, tissue repair, and clearance of brain waste via the glymphatic system.

Common disorders include insomnia, sleep apnea, restless legs syndrome, narcolepsy, and parasomnias. Poor sleep can impair mood, cognitive performance, and physical health. Good sleep practices—consistent schedule, a dark and quiet environment, and avoiding stimulants before bed—are associated with better sleep.