Questions: The sleep disorder characterized by acting out vivid dreams during a sleep stage when the body should be immobile is A) night terrors. B) REM sleep behavior disorder. C) narcolepsy. D) sleep apnea.

The answer is B) REM sleep behavior disorder.

Explanation for each option:

A) Night terrors: Night terrors are episodes of screaming, intense fear, and flailing while still asleep, often occurring in the non-REM stages of sleep. They are not characterized by acting out dreams.

B) REM sleep behavior disorder: REM sleep behavior disorder (RBD) is a condition in which a person acts out vivid dreams during REM (Rapid Eye Movement) sleep, a stage when the body is typically immobile due to muscle atonia. This disorder can lead to physical movements and vocalizations during sleep.

C) Narcolepsy: Narcolepsy is a chronic sleep disorder characterized by overwhelming daytime drowsiness and sudden attacks of sleep. It does not involve acting out dreams.

D) Sleep apnea: Sleep apnea is a disorder in which breathing repeatedly stops and starts during sleep. It is not associated with acting out dreams.

Summary: The sleep disorder characterized by acting out vivid dreams during a sleep stage when the body should be immobile is REM sleep behavior disorder (B).