Four Stages of NREM Sleep

Stage 1

This is the lightest stage of sleep, and it is easy to wake someone up during this stage. It is the transition between being awake and asleep, and it lasts for about 5-10 minutes.

Stage 2

This is a deeper stage of sleep, and it is more difficult to wake someone up during this stage. It is the stage in which the body starts to relax and slow down. This stage lasts for about 20-25 minutes.

Stage 3

This is the deepest and most restorative stage of sleep. It is the stage in which the body repairs and regenerates tissues, builds bone and muscle, and strengthens the immune system. This stage is also known as slow-wave sleep or delta sleep. It typically lasts for about 30-45 minutes.

Stage 4

This is the final stage of sleep, and it is the most difficult to wake someone up from. It is similar to stage 3 in that it is a deep and restorative stage of sleep. It typically lasts for about 20-30 minutes.