Not exactly following on from teta's post, but in case it is helpful for others, DD picked up a nasty bug a couple of days before her final exam (physics). High temperature, nausea etc. The school's advice was for me to march her to the GP, where the practice nurse confirmed in writing that she was very unwell. She then had to get up the next day and sit the exam, or as much as she could manage. She then stuck her hand up and was sent to the school nurse who was expecting her, and who was able to confirm again to the examination officer that she was very unwell.
She had no idea how she did, indeed had no idea whether she wrote anything coherent, or just rubbish. In the end she would up with an A rather than the predicted A*, but enough. My understanding is that the exam board can only award a small number of discretionary marks, so assume the point is to try and get as many as you can in the exam itself. The point though would be that she would have had something to present to the University had she narrowly missed the grade she needed. Another DS we know, kept quiet about the fact he had a flare up of a long term chronic illness, and missed his offer and place but a very few UMS, with a visible and massive drop in marks on the most affected paper. He got in on reapplication, and the University said they would have taken him first time round, but by the time they knew, all the places had been filled.
DD far preferred physics and maths exams to biology. The memorising was fine, but the getting down on paper was a problem.