Wait...so not eating for like an hour or so makes u have migraines? We don't eat every single second? I'm pretty sure it's possible I mean like I'm sure the room will be cooled, you'll be focusing on your exam not food, and you're sitting down...so I don't see how fasting would affect results? I've done many exams without breakfast and sat there for like 2 hrs and I don't get bad grades.
Of course unless you are aneamic or have a health condition or as u stated physically weak, then perhaps yeah I guess...but it has to be really bad, not like a ping in the head and then "that's it, I can't fast anymore".
If I get dehydrated or whatever I'll just ask to go to the bathroom to wash my face or get a bottle of water to through water at my face lol...worked last year.
I've watched Algeria against England (or was it Germany?) in the world cup and they were fasting whilst running around for 90 mins in a hot climate...they did well! 2-1 I think? Although England (not sure if it was germany) won as they are a stronger team but at least they scored a goal.
The footballers had wet towels instead of bottles of water.