There are four sleep stages identified by the American Academy of Sleep Medicine (each listed below with their alternate names) which are grouped by their classification as “non-REM” (NREM) and “REM”:
- Stage 1 (Stage NREM1 or Stage N1)
- Stage 2 (Stage NREM2 or Stage N2)
- Stage 3 (Stage N3, delta sleep, slow-wave sleep, SWS)
- Stage REM (rapid eye movement sleep)
Each sleep stage is categorized by neurological activity:
- Stage 1 features alpha waves and is the period of light sleep, wakefulness, and muscle tone when a person is first falling asleep.
- Stage 2 features theta waves and transitions between wakefulness and deeper sleep.
- Stage 3 Restorative Sleep features delta waves and is associated with stabilized glucose levels, testosterone, human growth hormone, and overall physical bodily restoration.
- Stage REM Restorative Sleep features rapid eye movement and rapid low-voltage EEG similar to when a person is awake. This is when a person dreams and is associated with cellular regeneration, cognitive restoration, memory allocation, and memory retention.
Adult humans generally progress through sleep cycles every 90 minutes in the following pattern, with more Stage N3 delta sleep found earlier in the evening and more Stage REM sleep found in the later morning hours.
When is Sleep Most Restorative?
Deep sleep occurs mostly within the first third of the night, while REM sleep occurs mostly within the final third of the night. This means that in order to get the restorative sleep your body needs from both deep sleep and REM sleep, you should be sleeping regularly for between 7 to 9 hours a night on a consistent schedule that includes regular bed times and wake times.
Both deep sleep and REM sleep can be affected by the habits and activities we engage in during the waking day, such as drinking caffeine or alcohol, or by exercising. Be sure to keep an eye out for any sleep stealers among your daily habits that could be chipping away at your restorative sleep.
How to Get Restorative Sleep