My cat Schmoo started having seizures at around 6 years old. Same thing as your beautiful Sheltie, it's a typical epileptic seizure, more common in dogs than cats.
Schmoo was on Phenyl Barbitol for a year and I then weaned her off because apparently it shortens their life by weakening their liver. She (knock wood) hasn't had one since, but she's always been a little nutty, zoning out and running around spazzy like on occasion.
I would at least have the dog checked out, but if he's not having them often there might be organic medicines than can lessen the severity of the seizures that won't hurt him.