Answer: A key symptom of REM sleep behavior disorder is a lack of paralysis during REM sleep.
Explanation: REM sleep behavior disorder is basically, a condition in which you act out your dreams while sleeping. They may include activities such as kicking, punching, arm flailing or jumping from bed, in response to action-filled or violent dreams, such as being chased or defending yourself from an attack. Typically one of the characteristic of REM sleep is muscle paralysis, this occurs because all the muscles are at rest. An individual having a lack of muscle paralysis during REM sleep is facing a disorder.