My CH cat Diva used to go upstairs, and when she tried to climb down fell to the bottom and had a seizure. She is not allowed up the stairs by herself anymore. At first blush I'd guess that Scout's seizure was caused by a knock on the head. But keep an eye out. The vet told me to do the same with Diva. She has not had one since she doesn't climb the stairs anymore.

Good luck!