The sleeper's eyes roll from side to side. If the eyes open, they do not see. At this point, although asleep about 10 minutes, a person if awakened might wonder if he or she had been sleeping or might believe no sleep had occurred. After about 30 minutes of sleep, stage 3 is reached. Brain waves are large and slow, rather like mountains.
Muscles are relaxed and breathing even.
This is the deepest sleep of all and lasts longer in the first part of the night than toward morning. Initially, after about 20 minutes of delta sleep, the sleeper ascends near waking again, but does not awaken. Instead, the sleeper goes into REM sleep, so named for the rapid eye movements which occur during this phase. The first REM period lasts about 10 minutes, and then the cycle begins again with the sleeper entering sleep stage 2. This cycle repeats itself about once every 90 minutes.