The stages of sleep are divided into two main categories: REM (Rapid Eye Movement) and NREM (Non-Rapid Eye Movement). NREM sleep consists of three stages: N1, N2, and N3. N1 is the lightest stage, where a person drifts in and out of sleep. N2 is a deeper sleep, and N3 is the deepest stage, essential for physical restoration. REM sleep occurs after the NREM stages and is characterized by rapid eye movements, increased brain activity, and vivid dreams. This stage is important for memory consolidation and emotional regulation. A typical sleep cycle lasts about 90 minutes, repeating several times throughout the night.