I have this dream constantly. Always that I forgot to ever go to the class, never that I'm struggling in a class or that I'm going to fail I class I've been attending. I wonder, did you skip a lot of classes in College?
In my case, there's some real-life precedent for it. I enrolled in one course in undergrad, and dropped it right away my first week or so for some reason I don't recall. Toward the end of the semester, before finals, I found I was still enrolled, but had never set foot in the classroom or anything.
I was sort of panicked, but went and talked to the professor, and he was fine with it. He basically verified that I never did anything with the class and it was somehow deleted from my record completely.
I still don't know why it wasn't dropped in the first week, although this was before electronic registration systems.