twokatz, that can be scary, I know. I don't have any experience with seziures in dogs, but our Monster started having seizures when she was about 6 months old. It started out with major drooling and twitches and after a few hours she went into a full blown seizure. Here, it turns out she found and played with the only ant trap we didn't throw away when we brought her home.
Now, according to the vet, every animal (humans included) is able to have a seizure, but each individual has their own tolerence level. They can be caused by something ingested, stress, lack of sleep, medication, any number of things. Seizures isn't a sickness, it is a symptom of something else and it could be a one time thing or something permenant. Heck, even I had a seizure one time when I was dehydrated and over heated. It can happen to anyone, and permanant medication isn't always the one answer.
Since his blood work came back fine, that is a good thing. You may want to talk to your vet about getting a prescription for mild valium. And, if he has another one start keeping notes about everything...what he ate, what he was doing, even the weather patterns. Valium alone didn't help Monster because there was some brain damage from the ant trap (and there were things in the blood work indicating that) which lowered her seizure threshold. But, we have realized that if there is a drastic drop in barametric pressure it will set her off (ie, a sudden rain storm or even heavy snow flurries). I have NO idea why, but if we see a storm coming we have to give her pheno and a valium. Also, if a lot of people are going to be around, she gets valium because she doesn't deal well with stress and it's best for her to just sleep through it.
But, this is worst case scenerio. I would talk to your vet again and see what he suggests and see if you can get some doggie valium just in case. Hopefully it was just a freak thing and not a permanant condition.