"Archie, a 50-year-old, has had a few episodes recently of physically acting out a dream while being asleep. Archie's wife has noticed these incidents and informed him about them. When they visit a docor, the doctor performs a brain scan that reveals neurodegeneration in the brainstem region. Which of the following diagnoses is the doctor most likely to make?
a. Narcolepsy
b. Somnambulism
c. Sleep apnea
d. REM behavior disorder