I usually dream that I am going into the exam right now, and am woefully underprepared.
In the dream, I can argue that the exams don't start for another month or so, but then they tell me that these are extra exams that I should have known about, and they count as well.
I open the paper, and the questions are ridiculous. I can't argue with this in my dreams, as it happens so often in real life, too.
Usually when I wake up the next day, I go and read a little about the scary topic from my dreams.
That is, if it is slightly relevant. If it is about purple elephants, anti-gravity time machines, or the krebs cycle, I just ignore it and go on with my usual work.