What Causes Seizures After A Fall On The Back Of Head?

Hi my son falls all the time as he is a boy and a dare devil. He has fell many many times and tonight he slipped on some water in the kitchen and fell on the back of his head. He was acting fine and has fell asleep now but I'm still worried. Also he has ferbile seizures and the first one was 20 minutes long can that cause brain damage? He sometimes holds his head and will scream for no reason.