I didn't read the whole thread but I had two dogs who had seizures. My half lab and my little shish-tzu who just left us.
Do you have your house and yard sprayed? That could be one of the reasons. Stick to one type of food for a while and monitor what he eats. Keep a tap on when he has them and what he did just before or where he was.
The thing is that the medicine he would take for seizures will also damage him....so check out some herbs too.....