Dogs having strokes?

Something went badly wrong with my 12 year old Lab today - she is epileptic - but today really lost her backend and orientation for several hours.  I was watching and observing and decided to go to the vet although she had been improving.  I had thought I might need help from the neighbour to get her in the car.  But when the appointment was made and ready to set off she actually jumped in the car unaided!  The vet found nothing much wrong except weakness in the backend - so its into observation now.  Previously I have had a dog with the same sort of symptoms who had a stroke and after helping her for what was - with hindsight - far too long - gave up the struggle.  Isn't it the worst thing about dog owning - knowing WHEN?