I would say count yourself fortunate. You didn't say if your son had this one isolated seizure, or if and I hope he isn't diagnosed with epilepsy.
My son had epilepsy. The first seizure was at the age of 5, and he did not have another until age 7, but then continued with seizures until he was 14. My son also had asthma, diagnosed at age 2, and continued with this illness until age 9. So, there was a (2) year overlap between each illness. Both illnesses were so severe that he was always hospitalized.
Once my son was hospitalized for a seizure and shared a room with a boy who also had epilepsy. It was during this hospital stay, that I realized no matter how traumatic this is for us, we are fortunate. This boys seizure activity was so severe that he had seizures at regular intervals, like every hour or so, which was not enough time for his body to recover. His seizures caused him to be mentally deficient. The poor child had to wear a helmet, spent most of his time in the hospital, unlike my son who spent a lot of time there. He rarely had visitors, except for his mom who stopped by only one of the (3) days we were there, and only for a 1/2 hour on that day.
Find a way to resolve the emotion and trauma of the event. While you're in despair, your child remembers nothing about the seizure, except what you explain. They can possibly explain the aura that occurs, immediately before the onset of the convulsions. You can contact the Epilepsy Foundation for information and support. Or you can stay in touch with me. I'm sorry if I sound hard, I don't mean to, but parents of a child who have had seizure activity have to resolve their issues quick and fast for their children. My son is 23 now and has been seizure free for 8 years..