Well what I do to stop the anxiety is think of things in a purely practical sense. Forget all the "I hope I'm lucky" and "I'm doing this for my future" crap. Think of yourself as a robot simply memorising facts, practising the output of those facts on past papers and then doing the real thing based on what you did with the papers while drawing on some facts you memorised at the same time.
Just think straight and don't worry about the consequences. At this time think of what the most effective method of revision is and just do it - play a game when you take a break or something - an optimum level of learning would be in 20 minute slots with 5 minute breaks. In the exam room as well, don't worry about not being able to answer, just move to the next question - on the other hand I also know that some people who find a question just slightly challenging just leave it and then they get scared because they skipped so many of them. Anyway, after you finish the exam go past the questions in a cool manner.
Finally, this may worry you a bit but - anxiety can mean a lot in terms of grades (it did for me at GCSE) so you really need to get over it... then again, you can always re-sit =)