Sleep is a natural state of bodily rest observed throughout the animal kingdom. It is common to all mammals and birds, and is also seen in many reptiles, amphibians and fish.

A sleep disorder (somnipathy) is a medical disorder of the sleep patterns of a person or animal. Some sleep disorders are serious enough to interfere with normal physical, mental ...

Definitions of sleep at Dictionary.com. ... Sleep Treatment Over-The-Counter Remedies May Not Be Enough: Learn About An Option

verb (used without object) 1. to take the rest afforded by a suspension of voluntary bodily functions and the natural suspension, complete or partial, of consciousness; cease ...

Fact sheet on normal sleep and sleep disorders developed by the National Institute of Neurological Disorders and Stroke (NINDS).