Glossary

sleep stages

Sleep is made up of 4 stages:

• Stage 1 — The lightest stage of sleep
• Stage 2
• Stage 3 — The deepest stage of sleep (slow wave sleep)
• REM (rapid eye movement) – Also called dream sleep

  • During this stage, you have dreams and rapid eye movements, and you can’t move
  • Your breathing and heart rate are less regular than they are in Stages 1 to 3

Stages 1, 2, and 3 are also called non-rapid eye movement (NREM) sleep.

In your first sleep cycle: As you fall asleep, you go from stage 1 to stage 2, then to stage 3. Sometimes you may go back and forth between stages 2 and 3. After that, you go into REM sleep.

While you sleep, you go through several cycles of all 4 stages. A typical sleep cycle lasts about 90 to 110 minutes. During later sleep cycles, your Stage 3 sleep happens earlier in the cycle and you have more REM sleep. For example, the REM stage in your first sleep cycle usually lasts about 10 minutes. Each later REM stage gets longer, with the final REM stage lasting up to an hour.

Usually, about 25% (one quarter) of your time asleep is REM. The other 75% (three quarters) is NREM.