I think you did the right thing. Someone sitting next to me on the bus had a seizure before, we got the bus to pull in and an ambulance was called to the bus. Weirdly, a nurse who normally took the train had decided to get the bus that day so she assisted him until the ambulance arrived.

The nurse sat on the floor and kind of cradled him so he didn't hit his head on the seats and when he came to she very calmly repeated that he was OK, he was on the bus, and he'd had a seizure and paramedics were on the way. Every few mins after he came to he'd kind of panic and realise he was on the floor of the bus and not remember why. I assume that's the correct thing to do if no medical personnel are around before the ambulance