I had my first seizure for no apparent reason, when I was 15yrs old. It was a grand mal and it left me with a horrifying headache, I was vomiting everywhere and I too, had absolutely no memory of what had happened.
That was 16 yrs ago and I have to say that my short term memory is fair at best these days, and my long term is just about gone... I can hardly remember my girls' childhoods (8&11yrs.) I don't know what wiped out the memory more, the seizures or the medications.
It's scary until you find meds that work, there are so many out there, don't settle if you don't have to for meds that make you miserable.