Funnily enough, I have the inverse of this dream. Exam-taking was never very stressful for me, so I never had the classic dream. But when I was a graduate student and started teaching my own classes, things changed. I, an inveterate procrastinator, started dreaming that that I'd shown up to the final without writing it. This, to me, is much more humiliating that blanking on a test. And I still have those dreams today, as well as a few variations (e.g., it's final grades time and I haven't graded any of the homework, or I've been supposed to teach a class but haven't remembered to show up for weeks).
