HPV Vaccine Reaction - Faint and seizure

My 17 year old son got an hpv vaccine today along with my 14 year old son. The nurse said please stay in the room for 10 minutes because the HPV vaccine can cause dizziness. My 17 year old son got it first. He felt fine and sat in the chair next to me. Then next my 14 year old son got his. He felt dizzy right away after the nurse left. So I told him to lay down and put his feet up. My 17 year old said he felt fine, so I was focused on the younger one. Next thing I know, my 17 year old face planted on the ground and started having a seizure. I was worried about him further hitting his head on the ground so I jumped on this back pulling up his torso/head/neck area...while screaming for help. 6 people entered the room and my 17 year old came to his knees and seemed to come to saying he was ok and then started convulsing again. I came behind him because I didn't want him to hit his head again. His body flung back and so him and I both fell back into the chair. Then he came to. Everyone in the room got him to the "bed" and my younger son who was already up from trying to help his brother then laid on the floor bc he was still dizzy.

The dr, without even looking at my 17 year old, came to me and said "he's fine! It's just an atonic seizure because he was probably holding his breath during the vaccine. But then I pointed out to him, he hit his head! So they brought him ice but I'm left still wondering. Was the seizure from the vaccine or hitting his head?! Any feedback would help! Except please do not bash me for getting the vaccine. As a mother, I've just had a day and can't handle that.