REM Behavior Disorder (RBD)
In REM Behavior Disorder (RBD) a person does not have this protective paralysis during REM sleep. A person therefore might “act out” their dream.
Since dreams may involve violence and protecting oneself, a person acting out their dream may injure themselves or their bed partner. The person will usually recall the dream, but not realize that they were moving in real life.
Normally in REM sleep, most of our body muscles are paralyzed to prevent us from acting out our dreams. In RBD, a person continues to have the muscle tone during REM sleep leading to behaviors where a person exhibits certain behaviors typical of RBD such as acting out the dreams.