it's perfectly normal, my way of dealing with it is to say "i've gone to the lectures, i've read the material, i've done the exercises and past papers and that's all i can do"
my general rule of thumb is i never revise or do anything the day before an exam (assuming the scheduling leaves me sufficient time), spend the day relaxing and making sure you're well rested, there's not much point staying up to midnight cramming as if you have to do that it's already too late and all you're going to do is make yourself tired.
the other thing is to remember that all you can do is your best, and there's a certain element of accepting that if your best doesn't cut it then at least you tried and you can live the rest of your life without wondering "what if i'd done that", if an exam is particularly hard and you're well prepared then it's quite possible it's just a hard exam and it'll get marked accordingly, i recall having a particularly brutal set of exams while on exchange in germany and yes it brought me to tears at the thought that i'd possibly fail at that point, but i just turned up did my best and it turned out that's just how they do their exams- hard papers easy marking.