I don't know about that actually, because you usually have to be put in 'quarantine' so you don't speak to others and get information about the exam paper. That means you might have to stay at a teachers house for a few days! Doubt it though. So I don't know what would happen with that tbo. But you should speak to the invigilator/teacher if you feel unwell and special considerations would probably be made (I don't know what those might be though). Maybe they would be more leniant or something when marking your paper.
Thats unfortunate though that you don't feel well, exams suck because if you don't feel well you still have to perform, hope you get better soon. Speak to the teacher or something.