Medical help? Witnessed a seizure today and have questions.?

Tonight my teammate/good friend hit his head very hard on a gymnasium floor at our volleyball game. He fell down and began to shake uncontrollably, foamed at the mouth, and his eyes rolled back into his head. A minute or two later he stopped shaking and opened his eyes but was extremely disoriented. EMTs arrived soon after and he is doing fine in a hospital now, but now I'm sitting here wondering how hard did he hit his head? I was on the court and heard something like a brick smack into the floor then turned around to my friend belly-up, convulsing. I haven't ever seen anything like that happen and it scared the **** out of me to be quite honest. After seeing him at the hospital I feel fine now but I can't stop remembering the image of him shaking on the floor. How hard do you have to hit your head to have a seizure? How long will he be out of school for and will he be able to remember anything that happened?