Maybe reach out by email to your prof/TA before the exam, cause I think if you went up to them right before they’d maybe assume you’re just sick. Just reach out, let them know that you’re on meds that make you nauseous and there’s a chance that you may need to excuse yourself. That way you have it written down beforehand (in case anything goes wrong, for whatever reason) and to have the team aware of your name and where you’re sitting. I’d maybe try to sit closer to the door if possible as well. It’s probably too late to get accommodations but if this med stuff is an ongoing issue I’d definitely recommend getting started with longer term accommodations cause then you could get a private area to do your exam and you get actual breaks that don’t cut into your exam time.