The sleep cycle is roughly 90 minutes long and repeats throughout the night. It's divided into four stages: Stage 1 (light sleep), Stage 2 (deeper sleep), Stage 3 (deep sleep), and REM sleep (rapid eye movement). Stage 1 is a transition from wakefulness to sleep, characterized by a slowing heart rate and muscle relaxation. Stage 2 is characterized by a further decrease in heart rate and body temperature, and the brain waves become slower and more regular. Stage 3, also known as slow-wave sleep, is the deepest stage of sleep, during which the body repairs and regenerates itself. This stage is crucial for physical recovery and cognitive function. Finally, REM sleep is characterized by rapid eye movements, increased brain activity, and muscle paralysis. During REM sleep, we experience vivid dreams and our brain processes information and consolidates memories.