There are two main types of sleep:
- Non-rapid eye movement (NREM) – also known as quiet sleep
- Rapid eye movement (REM) – also known as active sleep
NREM – Stage 1
- The beginning of the sleep cycle and is a relatively light stage of sleep.
- During this stage, the brain produces high amplitude theta waves, which are very slow brain waves.
- This period of sleep lasts only a brief time (around five to 10 minutes). If you awaken someone during this stage, they might report that they were not really asleep.
NREM – Stage 2
- People become less aware of their surroundings.
- Body temperature drops.
- Breathing and heart rate become more regular.
NREM – Stage 3
- Muscles relax.
- Blood pressure and breathing rate drop.
- Deepest sleep occurs.
- The brain becomes more active.
- Body becomes relaxed and immobilized.
- Dreams occur.
- Eyes move rapidly.