Look, the best thing you can do for him is to be upbeat, supportive, and optimistic. Children can bear a heavy burden of parental emotions ...
Can you help yourself feel better by taking action?
Go on the university website (you won't generally need a password) and see if you can find the exam regulations, so if he needs advice about how to appeal, or present after-the-fact mitigation, you can help him.
Advise him to contact his Department and his personal tutor. THey will help.
Is he receiving medical treatment for migraines? For them to happen like this suggests that there is a chronic problem there. He should contact the student health service. YOU can advise him of this.
You could also get the information about how he could make an application to have the chronic illness (migraine) noted in his student records, and help him to organise a discussion with his university's student services to look at whether there's a need & a case for 'reasonable accommodation' of his chronic condition at exam time.
You can't contact the university directly about these things, but you can guide him towards learning how to represent himself effectively. You can lead him towards resilience & confidence. To do that would be a marvellous thing to do for him.