sleep

a state of lower awareness accompained by reduced metabolic activity and physical relaxation. When falling asleep, there is a change in the brain's electrical activity, which can be recorded by an ELECTROENCEPHALOGRAM ( EEG ). There are high amplitude, low frequency waves (slow-wave sleep) interrupted by short periods of low amplitude, high frequency waves. The periods of high frequency waves are typified by restless sleep with dreams and rapid eye movements, hence the name REM SLEEP , and the EEG is similar to that of a waking person. REM sleep comprises about 25 percent of the time asleep.