to be honest... panic attacks are pretty common. and u can train
to overcome it. i actually get panic attacks like, about 30 minutes
before my races, sometimes even when i'm sitting on the grid
waiting for the race to start. what i do is, i force myself to
breath slowly and deeply, and calm down. when my race starts, i
focus on the race and push everything that was worrying me out of
my head.
try my method of breathing slowly n deeply to calm down, and simply
focus on your exams when it starts, and do not think about anything
else until the paper is over.