Four-year-old DeMarcus falls asleep shortly after his 8:30 P. M. bedtime. At about 9:45, he suddenly sits up in bed, breathing rapidly and appearing to be in a state of sheer panic. He doesn't remember anything about the episode upon waking. DeMarcus is experiencing: a) a nightmare. b) a narcoleptic attack. c) sleep terrors. d) REM sleep behavior disorder