Sleep occurs in frequent periods, in which the body alternates between two different modes: REM sleep and non-REM sleep. Although REM means "rapid eye movement," this sleep pattern has many other aspects, including virtual paralysis of the body. Dreams are a series of images, thoughts, emotions and sensations that usually occur involuntarily in the mind during certain stages of sleep. During sleep, most body systems are in an anabolic state, which helps restore the immune and nervous systems and the