During rapid eye movement (REM) sleep, skeletal muscles are almost paralyzed. However, in REM sleep behavior disorder (RBD), which is a rare neurological condition, muscle atonia is lost, leaving afflicted individuals free to enact their dreams. Although this may sound innocuous, it is not, given that patients with RBD often injure themselves or their bed-partner. A major concern in RBD is that it precedes, in 80% of cases, development of synucleinopathies, such as Parkinson's disease (PD). This link suggests that neurodegenerative processes initially target the circuits controlling REM sleep. Clinical and basic neuroscience evidence indicates that RBD results from breakdown of the network underlying REM sleep atonia. This finding is important because it opens new avenues for treating RBD and understanding its link to neurodegenerative disorders.