eople with rapid eye movement (REM) sleep behavior disorder act out their dreams. While sleeping safely in bed, for example, they might throw up their arms to catch an imaginary ball or try to run from an illusory assailant. Such actions are more than just a nuisance. People with the disorder have a 50% to 80% chance of developing a serious neurodegenerative disease within a decade of diagnosis. CLICK TO REVIEW ARTICLE