Your grade is based on your final. If you think you will feel ill on the final, it will be shown on the curve when compared to those who were not ill in their studies and/or the exam. I know. One of my finals I had dissentary. Spent more time in the bathroom, running to bathroom, and sitting their wishing I was in the bathroom than focused on the exam. Not the same deal as yours I know, but a good example.
I recieved my worst grade ever in that exam (D) which is a "pass" in theory but only because I did ok on the other exams that were luckily scheduled several days latter. That was after being in good health to prep. If I'd been ill before and during, I would've failed for sure.
Just a thought. Lost money vs lifelong impact of grades on GPA.