How to know if your dog has had an epileptic seizure

  Today was a really scary day but a learning experience. 

It started out normal until my dog Rivet came in from going going outside.I noticed as he walked he was wobbly. I gave him his potty treat and as he walked to eat it under our dining room table-his favorite spot to bring his toys and treats I noticed something wasn't right. I thought its hot maybe he got overheated. I went to bring him to his water and he went limp-I held him, then he wanted to go in his crate. Then he went to the door to go out and did number 1 and number 2 but instead of coming in he went to sit in the shade close by. I realized he didn't have the energy I picked him up and brought him inside. Before I knew it he started crying like I've never heard before his eyes went cloudy, his neck were cocked back and he started to stiffen...I thought he was dying in my arms...it was horrible! My son Blake came down and held him while I got dressed to get him to the vets.
Once we got to the vets he started getting more of his wits back but lost his functions in my sons lap.
We had done yard work and I was worried he ate some of the preen we put down or some of the wild weeds.
The doctor did blood work and he has epilepsy. They are holding him until 5 PM for observation and to get him to pee for a test. They say with medication he can live a normal life-yeah! It is usually detected around 2 years old which is what he is.
He had signs before but never this severe we had mentioned them to our other vet but we were trying different foods. We thought it was maybe his food so we searched for healthy ones- it seemed to us like his blood sugar was out of balance because he would get week when he got too excited-but now we know it is epilepsy.
I am going to ask the doctor when we pick him up what is the best thing to do when he has an episode and I will post it. Also the medication they give him.
They said to comfort him-there is not much you can do and keep his mouth away because they might bite not meaning to-they don't have control. If the episode lasts longer than 5 minutes take him to the vets or Emergency Pet Hospital.
The medicine they gave him is a generic version which is not harmful to his liver and less expensive. It is called Levetiracetam 250 mg. 1/2 tablet twice a day for life.
My son said at least its just epilepsy and then he looked at me like did I just say that? But we are thankful he is still with us and will have a good quality of life:) We will hold him a little tighter tonight and are thankful:)