[Sadrain]

It's stressful situation, you admit it or not, and getting sick for your body is kinda self protection because even if being sick is troublesome, you don't have to go out and be among the things that cause you stress (and other things). At least, it can be one explanation as to why you get sick then - your body weakens your immune system on purpose in a way and so you get sick. Other people, if they press on, get "ghost pains" that are strong enough to literally keep them down into the bed and other things, or combos of them. It all depends on the person.
I am honestly surprised I have managed to get this far without falling sick, like in 2nd week of school, but... If I did it this far, I should hold out trough the next week. I need those marks. Ugh.

EDIT: Of course, it can be just change into daily rythm and such to cause you to get more sick then, or other things, but I am just taking the version that I know the best from personal experience.