REM behavior disorder is primarily characterized by_________________.

REM behavior disorder is primarily characterized by a lack of atonia, which is the normal paralysis that occurs during REM (Rapid Eye Movement) sleep. In healthy individuals, this paralysis prevents movement while dreaming, thereby safeguarding them from acting out their dreams. However, in individuals with REM behavior disorder, this atonia is absent or diminished, allowing them to physically act out their dreams. This can endanger the person or their sleep partner due to potentially violent behaviors.

The other options pertain to different sleep disorders or conditions. Excessive daytime sleepiness is more often associated with conditions like obstructive sleep apnea or narcolepsy, while a lack of dreams does not accurately characterize REM behavior disorder, since dreaming still occurs but may be enacted upon. Restless legs syndrome involves uncomfortable sensations in the legs, often leading to an urge to move, and is a separate condition unrelated to the behaviors seen in REM sleep.