Feline epilepsy

Thompson is a 2 year old male. He was 4 months old when we first brought him home. He had a seizure a month later. I promptly took him to the vet. They examined him and did blood work etc but found nothing. We figured he hit his head.
More than a year later he had another seizure. He came flying up the stairs and had a seizure in the kitchen. He had nothing for a month and now he's had 3 seizures 30 days apart.
They are grand mal seizures that last about 30 seconds. He salivates and sometimes pees. He recovers quickly and goes about his day!
Does anyone know how frequent the seizures usually are before they will treat with phenobarbital?
I mentioned Thompson's seizures to the vet tech the last time I was there for my other cat and she said to keep track of the frequency, duration, etc. She kind of shrugged her shoulders but I think she said something like if they were more than once a month?

Thanks for the help!

Bumping this in the hopes that someone with experience with epilepsy will chime in. 
[article="22453"]Cat Epilepsy  [/article]

I guess it is a little different when your vet has seen Thomson from 5 months when he had the first seizure you knew about, but if this was me I would want the vet seeing my cat again so I could talk through what I have seen when there seems to have been an increase in seizures.   Go for a vet consultation and don't be put off by the vet tech'.

Is your cat indoor only so you would know if there were other seizures happening even if no one was around to see them?   The kitten that lived in a house I shared with others many years back would soil if he had seizures but no other time which is how we realized something was up.   They were happening every few days and turned out to be due to a virus and deteriorating rapidly which will not be the cause for your cat.   However, every month or so is more often than I would like and if a vet can check again to see if there is some cause, and also determine the what would be the best way to control the seizures (if they think necessary) then that has to be good for your cat.

A friend of mine's elderly cat started to have seizures about 5 years ago and they got more regular over a period of a few months.   Once he started on medication for them the seizures were well controlled and they felt able to leave him alone in the house without worrying, and for neighbours to watch over him if they went away for a few days.