Light sleep; easily awakened; muscles relax with occasional twitches; eye movements are slow.
Eye movements stop; slower brain waves, with occasional bursts of rapid brain waves.
Occurs soon after you fall asleep and mostly in the first half of the night. Deep sleep; difficult to awaken; large slow brain waves, heart and respiratory rates are slow and muscles are relaxed.
* Usually first occurs about 90 minutes after you fall asleep, and longer, deeper periods occur during the second half of the night; cycles along with the non-REM stages throughout the night.
* Eyes move rapidly behind closed eyelids.
* Breathing, heart rate, and blood pressure are irregular.
* Dreaming occurs.
* Arm and leg muscles are temporarily paralyzed.