The state of lessened consciousness, reduced metabolism, and limited activity of the skeletal muscles that we call sleep and the problems and disruptions associated with it. Not a single, uniform state, sleep goes through stages, which can be recognized on electroencephalographs (EEGs). The two main, alternating stages are named for their primary characteristics: NREM (nonrapid eye movement) and REM (rapid eye movement), during which dreaming occurs. Adults generally start with a period of NREM sleep, which then alternates with short periods of REM sleep throughout the night. Infants, on the other hand, tend to start with REM sleep.