Seizures can be caused by so many things that the only safe thing for you to do is take your dog to your vet and explain everything to him. Please don't worry, most cases can be controlled with drugs, many cases have been having very minor fits in their sleep all their lives. There are a lot more fitting dogs out there than anyone realises. It may be a one or two fit thing that will never happen again or it may be an ongoing thing. It is a huge area and the only thing to do is let a vet take control. The age of your dog suggests that medication will be needed, but, again, they are all different.