Like many people, when I was a student, I used to have nightmares where I found I had to take a final exam in a class I did not remember being in. (One particularly vivid one also involved discovering a new building on the Berkeley campus, between Evans Hall and Le Conte.) When I became a teacher, this flipped around, and I had sporadic nightmares where I was giving an examination in a class I didn't remember teaching. Thankfully, it's been several years since that one last visited me.
After watching this xtranormal movie from my friend Cris Moore, I suspect that I will have nightmares about examining students in subjects they did not know they were taking:
I hasten to add that, to be the best of my knowledge, nothing like this has ever happened in this department.