Yeah, I'm starting to feel it too, and I've taken the stupid thing before!!! I've spent a whole lot more time studying this time around and I'm just worried that I'll make the same score and all this time will have been wasted. I blew my whole spring break studying for this, it better be worth it.
It really just helps me to channel all my nervousness into an overriding focus. That's just the way I handle stress: I use all the bad nervous energy for the good purpose of studying. That way I get something accomplished and hopefully fell more confident about how I'll do. I don't know if that's practical advice or not, though. Oh well.