Which of the Following Scenarios Exemplifies a Nightmare

Which of the following scenarios exemplifies a nightmare?

A) Joey starts blabbering early in the night but seems to remember nothing when he wakes up the next morning.
B) Christie starts climbing the stairs early in the night and seems oblivious to her surroundings.
C) Jason wakes up very early in the morning, knocks at his parents' door, and starts to cry uncontrollably.
D) Kellie screams and sits up on her bed in the middle of the night and goes back to sleep after a while.