I’ve been pondering how fear responses are, in many ways, the same as arousal responses. Also, many people, particularly those with submissive tendencies, are aroused by situations in which they are powerless, just like many nightmares.
So I’m wondering who has become massively aroused by a nightmare that was also terrifying. What was it that you dreamed about and how did you feel about it when you woke up?

Maybe similar to the suspended bridge effect.
Fear of death being tied to preservation of the species so you want to pass on your genes.