Main Content
What you will learn in this section:
People normally sleep in cycles during the night that involve 2 states of sleep:
There are 4 stages of sleep—1 in REM and 3 in NREM. Dividing NREM sleep into 3 stages is pretty new, so you might still see books or articles that talk about 4 stages of NREM sleep.
During sleep, people move back and forth between NREM and REM sleep. This normal shifting back and forth between sleep states is called sleep architecture. A special graph called a hypnogram (see below) shows a person’s sleep stages.
Read about the different states of Sleep below.
Stage 1 (transition stage)
Stage 2 (light sleep)
Stage 3 (deep sleep, slow wave sleep)
During REM sleep:
Why do people dream?
Research shows that dreaming improves memory, learning, and problem solving.