That happened to me in my Maths. I panicked so much that I couldn't stop shaking and I kept dropping my pen. Needless to say, I ran out of time and didn't even finish the paper.
The exam after that was psychology and I managed well for it. I think the trick is to tell yourself that the exam is not that difficult. Deep breaths before the exam and during it whenever you feel stressed helped me a lot to relax.
Remember you've revised so don't stress when actually doing it.
Hope you all the best for your exam