GTT test at 28 weeks.

So in exactly 15 days I got to do my GTT, I've never had to do one before so it's all new to me. I know I've got to fast the night before so no food and only water after 10pm. I'm just worried about the result. I was in hospital today because of a insanely bad migraine to the point my vision was going black, the Dr told me there isn't anything wrong and was sent home but I still can't shift the migraine. I don't know if it could maybe be linked to GD? I'm just a bit worried, this is the first baby I've carried this far after 3 miscarriages last year so anything that's slightly wrong I panic a lot! I'm guessing it's a two hour one as I'm fasting the night before. Any help would be brilliant! Thank you Ladies ❤