Q. My cousin says she was diagnosed with REM Sleep Behavior Disorder. Have you ever heard of such a thing?

A. Actually, yes. According to some sources, this sleep disorder, in which the patient acts out the dreams through limb movements and talking, is very rare (reportedly fewer than 20,000 cases per year are identified in the USA). The exact cause is unknown but there are several risk factors (e.g. neurodegenerative disease, drug withdrawal, and narcolepsy). Symptoms include limb movement (e.g. arm flailing, talking and laughing, ability to recall the episode). You might like to review what the Sleep Foundation says about it.