I dont have it quite that badly, but I always get really anxious before a big exam and forget stuff. Ill usually sit the entire exam time going over everything again just in case something else comes to me, which it usually does.
Try relaxing an hour before your exam and play video games or something and just dont even think or worry about the test. Worrying about it wont do you any good. I think relaxing beforehand is key. I try and just mellow out before an exam and not cram. And be positive about the outcome and tell yourself you have it all dialed.
That stuff helps me so maybe it will help you homie