See if you can explain this

It's almost 4 AM and I'm bored so I figured I'd ask.

I have neurocardiogenic syncope, but I didn't know this until a recent tilt-table test. For years I've been on phenytoin for what was (as anyone's best guess) diagnosed as a seizure disorder. My first NCS spell in '03 did produce what appeared to be a seizure, but only that one time. I was not on any medication at that time.

As far as I've been told by the RN who did my tilt-table test and the pharmacist at my work, phenytoin is never prescribed for NCS. When I was on 100 mg once daily, I had severely increased NCS-like symptoms (nausea, dizziness, etc.) and even two spells within the span of a week. I was bumped to my current dosage after that.

I'm on 100 mg twice daily and it has kept the NCS spells down (aside from the tilt table test, which induced a spell after administration of the nitro tablet). My last spell was in January and I was on my current dosage at that time. I chalk that one up to stress from school.

So can anyone explain why an antiseizure medication keeps me from having NCS spells?

I go to my neurologist next week to discuss this, but I wanted to see what you guys and gals may come up with. I'm very interested in hearing what you have to say.