I totally understand your concern, I think alot of people including myself suffer from a bad memory. I can remember all too well nights before exams going through work at 10 o clock at night thinking "I don't remember that" but as long as you have revised, there is nothing to worry about. The exams were not designed to trick us, they tried to help jog our memory. As Smudge said, you certainly don't sound unintelligent. I think you are stressing too much about this, as practically everyone else is, but we must do our best to distract yourself from thinking about it, for example I've started playing squash, walking the dog and bicycling.
What I'm trying to say, relax, as long as you put in the 100% effort which is plain to see that you did, that WILL show in these exams. Good luck.
Ps. Welcome to the boards!