After N3 sleep, people cycle back to lighter N2 sleep before going into REM sleep. People cycle though the stages of NREM sleep 4 or 5 times each night and enter REM sleep several times during one night. Dreams occur during REM sleep and the eye move quickly beneath closed eyelide. During REM sleep, people and animals are paralyzed. Scientists think people enter a state in which they cannot move so that will not hurt themselves while they are dreaming.