NREM sleep, or Non-REM sleep, is the first part of your sleep cycle and includes three stages. Stage 1: For about 5 to 10 minutes, your body is in a state of “light sleeping”. Your eye movement and muscle activity begin to slow down. Stage 2: At this stage, your eye movement stops, your heart rate slows, and your body temperature decreases as your body prepare to enter deep sleep. Stage 3: This stage is deep sleep where your brain produces delta waves (very slow brain waves). Non-REM sleep contributes to your overall health since during these stages, your body build muscle and bone, repairs and regenerates tissue, and strengthens your immune system. As you age, you don’t get as much NREM sleep.