Doctors say that people have five stages of sleep and that they usually go through each phase about every 00 minutes. During the first two stages, you sleep lightly. If someone calls you or puts his or her hand on you, you wake up quickly. Your body rests quietly. You breathe more slowly than when you are awake. Your heart beats slowly. During stages three and four, you sleep deeply. If someone puts his or her hand on you, you don't wake up. Your heart beats more slowly than it does in stages one and two. Neither sounds nor lights wake you up. The last stage of sleep is called REM (Rapid Eye Movement). During REM sleep,