Non-REM sleep is a phase of sleep that does not involve rapid eye movement. It is divided into three stages, ranging from light sleep to deep sleep. During this time, the body undergoes important restorative processes, such as tissue growth and repair, and the immune system strengthens. In non-REM sleep, brain activity slows down, and heart rate and breathing become more regular. This phase is crucial for memory consolidation, helping the brain process and store information from the day. Overall, non-REM sleep plays a vital role in physical and mental health.