Scientists are not sure of all the reasons for sleep. They know that sleep helps the body heal and grow. Sleep helps the immune system – which helps people fight disease. Sleep helps the infant brain grow. It seems that REM sleep is especially important for babies’ brain growth. It also seems that sleep is a time for processing memories. Why do we dream? Some scientists believe that dreams have a psychological purpose. Some think that dreams help organize our brains. Some think that dreams are the result of random brain activity during REM sleep.