Paint your nails! It doesn't take too long and there's something about the process that is just so nice and calming. Plus, you'll have a cute look for exam week! (Also, grab a coffee! I always need caffeine during these times...)
Take a bath! I love using the Lush bath bombs; they're great and smell delicious! (Or: add tea bags to your bath; it supposedly is very relaxing.)
Do some yoga! You don't have to do anything crazy; just a few stretches would help. I also find that after a super stressful day, stretching my arms and legs before bed really helps me get to sleep quickly.
Brush your hair! This may be the quickest one on the list, but it's definitely effective. (I also find that washing my hands is a quick way to get energized.)
Hope these help!