Is It Safe To Fly With Headaches From Hitting On Head?

We are vacationing in France and my 18 year old son was out drinking night before last with his friends and slipped on the cobblestones and hit the side/back of his head. His friend says he was unconscious for about a minute. They boys didn't mention this when they came in that evening so my son went to bed and slept 8-10 hours, which is normal for him. He still has a headache. There isn't much of a bump where he hit his head, and there are no cuts or bruising anywhere on his head or body. He does have a slight bit of swelling (I think) at his left temple and continues to have a headache. He rates his pain at a 2-3. We are scheduled to fly to Ireland tomorrow evening which is a 2 hour flight and we are wondering if it's safe to fly. As well, should we take him to a hospital? I might add, this is my one child out of three that has had any serious injuries so I'm a little quick to take this one to the hospital (my husband thinks he's fine); he has had 2 broken arms, a broken nose and 2 broken wrists from skateboarding (he finally gave it up!) and is concerned about flying.Thank you in advance for your advise,Mrs.O'Connell