what is sleep

Sleep is a complex and essential process during which the brain and body engage in various activities necessary for life. It is a state of reduced mental and physical activity, during which consciousness is altered and sensory activity is inhibited to a certain extent. Sleep is not a passive state, but rather a highly active process during which the brain processes the days events and restores energy. The brain cycles repeatedly through two different types of sleep: REM (rapid-eye movement) sleep and non-REM sleep. Sleep is important for a number of brain functions, including how nerve cells communicate with each other, and it plays a housekeeping role that removes toxins in the brain that build up while awake. Sleep is also vital for the rest of the body, affecting almost every type of tissue and system, from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. It is regulated by two main processes: circadian rhythms and sleep drive, and a chronic lack of sleep or poor quality sleep increases the risk of various disorders and health problems. Overall, sleep is a necessary and active behavior that is essential for mental and physical health.