NREM sleep includes three different stages, namely stages 1, 2, and 3. The transition from wakefulness to sleep occurs during the NREM 1 phase. In NREM 2, brain waves slow down even more. Eye movements are no longer visible, and all the muscles are relaxed. In the NREM 3 phase, the brain waves slow down so much that it almost shows the brain wave activity in a coma. This phase is the hardest to wake up.
