I have been diagnosed with Epilepsy and on Dilantin for ten years. I have had the experiences you are talking about, and they are frightening, I know!
The first time I had it I thought I was going to die. I was actually alone in my room thinking about my child and my husband, crying asking God not to let me die. This is a scary thing, but I am still here. I have continued periodically to experience these episodes, but nothing ever happens. I too went for testing, and the doctor could not understand what I was talking about let alone try to figure it out what was causing it.
Do you know what I thought it was? An inner ear infection. I had severe vertigo, and every time I raised my head above a parallel position the dizziness got worse. My docotor said that dizziness, side to side was normal, but vertigo, falling backward was not.
Don't be frightened, but do seek your docotor's opinion. He may have some insight where mine did not.