Scientifically speaking, what causes someone to have images of horrible torture being inflicted on them in their head whenever they're trying to fall asleep?
What causes them to be periodically sprung back "awake" when they're drifting to sleep because they saw some sort of scary figure, or in some cases just a regular image that completely terrified them for no reason while their eyes are close?
What causes someone to be so afraid of the dark that they always have a knife within a few inches of them at night?
Asking for a friend...