Stages of Sleep

Quality of sleep

• Stage N1—drowsiness or somnolence

• Stage N2—superficial sleep with a decrease of muscular activity

representing 45%–55% of total sleep time

• Stage N3 (deep or slow-wave sleep)— deep sleep, as evaluated by the delta activity; parasomnia, such as sleepwalking, sleep-talking

• REM sleep, also known as paradoxical sleep or dreaming—accounting for 20%–25% of total sleep time in human adults and being the last part of a sleep cycle of 90–110 minutes

• Sleep timing