Hi There

I know how scared you must be feeling right now. My border collie, Finn, had his first fit when he was aged 4. He's now 10 and takes medication twice a day and is very well controlled.
Yes, it is possible for a dog to only have one fit. In fact, my youngest dogs mother had one fit aged 5. She was spayed and, 2 years on, has never had another fit.
All your vet can do at the moment is a blood panel to check for any abnormalities. As infection can also cause seizures, I would also be inclined to carry out the usual urine and temp tests. If all shows as normal....it's unfortunately a waiting game to see if any other seizures occur. Epilepsy is only diagnosed following repeated seizures and the absence of any other abnormalities.
In the meantime, I would consider your dogs diet. There is some evidence that preservatives in dog food can lower the seizure threshold (causing seziures in lab rats).
I would also think about leaving your dog in a separate room from your other dogs when you go out. Dogs have been know to attack a seizing dog - mainly through fear. Also, a dog is very disorientated following a seizure and may show signs of aggression both towards yourself and other dogs they know well. I truly hope your dog has no further seizures but, if so, just allow them their own space to orientate themselves (allow them to approach you rather than approaching them - Finn used to sniff me to death before demanding a very large reassuring hug!). As seizures are very energy consuming for a dog, I used to keep a little organic ice cream for Finn to have a small amount of following a seizure. Don't allow solid foods immediately following a fit, this is in case they go into a repeated seizure and there is then an increased chance of choking. About an hour after a fit, I would give Finn a small amount of his normal food for a more sustained energy release.
Lastly, I read some dreadful stories on the internet about epilepsy in dogs. So, if the absolute worst happens, please don't despair. Finn is very well controlled and, aside from a little bit clumsy and trembling back legs from the medication, he has the normal lust for life that you would want a dog to have

xxx