Dreams.

I woke up three times during the night in a cold sweat. I installed the quest mod Clockwork Castle for Skyrim – the one where the paintings of our artists are displayed in the Haven. There's a rather creepy location in it, and an even creepier ghost woman who pursues the player and, at some point, starts flying around them with wailing sounds and draining their life. For my level 89 champion, it's nothing; he didn't even use healing, but it's very unnerving. And yes, I played for a while, and then I dreamed that this woman was chasing me.