Sleep is a period of rest during which the sleeper loses awareness of his or her surroundings. When a person falls asleep, all activity decreases and the muscles relax.  The heartbeat and breathing rate slow down.  The person slowly becomes less aware of what may be happening all around. The two major stages of sleep are the non-rapid eye movement (NREM) or resting stage and the rapid eye movement (REM) or non-resting stage. The REM stage is al