Acting out dreams during sleep is a warning sign for REM sleep behavior disorder. It causes you to act out vivid dreams as you sleep. The dreams tend to be action-packed. You may punch, kick, jump or get out of bed and run. All of this occurs while you are still asleep. Injuries during these events are common. Normally your brain paralyzes most muscles during the stage of rapid eye movement sleep. REM sleep is the stage of sleep when you have most dreams and nightmares. REM sleep behavior disorder occurs when the brain fails to tell the muscles to remain still.