I have a friend who had panic attacks every time he fought. He lost his first 9 fight (almost all by RSC in the first round) because of it.
He went to therapy for a year to get over it and finally got a prescription for beta-blockers and those seemed to work.

I find for me, if I KNOW for certain that I've done everything and then some that there is NO WAY that my opponent has put in as much time and effort as me, that really helps.