ameyers6,IMHO, I think it is a good sign that with below therapuetic levels of Dilantin you have not had another seizure in 15 years which makes me wonder if your dx. may have been wrong as far as what caused your seizure. Of course, you know I am not a Dr. but repeating the EEG sounds like a good idea.
Extreme anxiety can cause a person to shake or appear to be in shock, which mimics what happens during a seizure. Since anxiety attacks and epileptic seizures appear so similar, it is difficult for a layperson to tell the difference.
I had one seizure 46 years ago and was on Phenobarbitol for years until I just stopped taking it on my own and I never had another seizure. My EEG result was "unknown etiology" - in other words the EEG did not confirm epilepsy or any other cause for the seizure.
I hope your EEG comes back normal.
Kindly,
Kitt