You should take your dog to the vet ASAP to get checked out. If a dog has more than one seizure in a 24 hour period, it is known a seizure cluster and warrants an immediate vet trip. It is very unlikely this is actually life-thretentaning if the seizures are so short and he is fine afterward, but it is good to get him checked out. It is totally possible that the flea preventive could have caused it, though it is hard to know for sure. I would recommend switching him back to frontline, or talking to your vet about alternative preventions. Do not use any alternative preventions, such as garlic, without checking with your vet first. Garlic has the potential to cause problems if given in large amounts.
The vet will probably do blood work to check the Kidney(or liver, I forget) functions, and if those come back normal they may prescribe a medication like Phenobarbital. These meds often take several weeks to have full effect.
I once had a foster dog with Epilepsy, but he had Focal seizures instead of grand mal ones.
