My main worry was always hypos (my levels drop when I'm stressed), so I always had a sugary drink or some unwrapped sugary sweets on the desk next to me so I could quietly munch if necessary. If you're likely to be high maybe ask to bring your insulin in if you're on injections and just ask to be excused/do it subtly if needed. Also my schools and uni always had a smaller exam room for people who needed extra time or special conditions, and I asked to do my exams in there as it was easier to get me out if something did go wrong, and also I found it less stressful than the main hall so my levels tended to be marginally more stable. Best of luck! Rachel x