NREM sleep, or Non-Rapid Eye Movement sleep, is a crucial phase of the sleep cycle that consists of three stages. It is characterized by slower brain waves, reduced heart rate, and decreased muscle activity. During NREM sleep, the body focuses on physical restoration, growth, and immune function, making it essential for overall health. The first stage of NREM sleep is light sleep, where a person can be easily awakened. The second stage involves deeper sleep, while the third stage, known as slow-wave sleep, is the deepest and most restorative phase. Together, these stages help the body recover and prepare for the next day.