asleep

Asleep is an adjective describing a state in which a person or animal is in sleep, or a related adverb meaning in a sleeping state. It indicates reduced consciousness and responsiveness, typically with sensory input and voluntary movement diminished. The term is commonly used to describe people, animals, or even machines that are not awake.

Etymology traces asleep to Old English aslǣp, from a- plus slǣp, meaning sleep. The form evolved into modern English as the standard word for the state of sleeping. It is usually used with a subject, as in “the child is asleep,” and often occurs in phrases such as “sound asleep” or “asleep at the wheel.”

In humans, sleep is a natural, reversible state of reduced consciousness governed by the brain. It cycles through stages N1, N2, N3 (deep sleep) and REM sleep, with cycles typically lasting about 90 minutes. An average adult spends roughly 7 to 9 hours asleep in a typical night, though requirements vary by age and individual needs. Sleep supports processes such as memory consolidation, metabolic regulation, and restorative functions.

A person who is asleep is not the same as being unconscious due to anesthesia, a coma, or a medical condition. While sleep and these states share reduced awareness, they involve different physiological mechanisms and levels of controllability.

Common usages include phrases like “sound asleep,” “fall asleep,” and idioms such as “asleep at the wheel.” See also sleep for related topics on the cyclical nature of sleep, its stages, and factors that influence sleep quality.