Sleep

Bodily state of rest when there is little or no conscious thought or voluntary movement is called sleep. Every human being is requires a minimum hours of sleep to keep the body function normally. Electrical waves recorded from brain show, sleep occurs in cycles of around two hours; in a cycle there is a period of intense electrical brain activity and rapid movement of eyes under lids (REM) followed by longer session without REM. Dreaming occurs during REM and appears to be a necessary mental process.