Writing 4 exams this week in math / computer science, I am super nervous. Any tips to stay calm? :)

Focus on what you know, it's more than you think.
Breath.
Always rely on the process.
Check your work.
Remember, no one dies if it doesn't go well.
There's always money in the banana stand.

Weed.

NZT-48 can be a solution.

You should have a ~20min walk right before the exam starts. That will give your brain fresh oxygen and will decrease the likelihood of having a "blackout".
Seriously, try it !

Just don't give a fuck. It's an exam, a piece of paper you use to proof to some old guy that you studied like a good student. If you learned something during your semester that you'll take with you you've already done what you are there to do. You study for yourself, no one else. Making some prof believe that you know your shit should afterwards be the easy part.

Thinks about puppies or kittens

I would say this:

Remember to remember that you actually know what you know.

You studied, you did the work, you were able to figure out answers to problems, etc. You now KNOW that which you studied. Don't forget that because you're nervous. It's easy to do so, I know, but you got this. You aren't walking into a foreign environment. You're going to just answer questions to things you already know.

In my uni if one of our housemates died or someone died during an exam we were in we got a pass for the year or a pass for the exam.

Don't take one for the team :L