I had the same problems during the first year of my med school. Later on I lost the fear of the exams and I dealed with them pretty well. However, I can understand you very well.
I'm sure that anyone who hears about your problem tells you to relax and get the bad thoughts out of your head. Easy to say, harder to implement. But the more you think about relaxing, the less relaxed you actually are.
The only succesful way would be the pharmacological way. Try the extract from the hop cones, can be bought in every pharmacy. Pump yourself with a big dose and deal with the exams. Should work.
There are also plenty of other agents, but this one should be the first choice in this case.