Should I Get a Second Opinion on My Fainting Episode?

should I get a second opinion? so long story short, I was at work and stood up after sitting down for a while. no I have had experience fainting after standing up and I even got a concussion from it at one point. but this time when I stood up, I remain conscious as I fell and I started convulsing on the floor for about 20 seconds. I was conscious during the entire thing, however, that has never happened to me before. so I went to the doctor and they told me that I probably just had low blood sugar and to make sure I eat if I'm dizzy. I have never had any blood sugar problems before, and I tried to explain that but they kind of just dismissed it and left. like I said this isn't the first time this kind of thing has happened but I am a bit concerned because I have never convulsed like that before. am I being excessive, or should I get a second opinion on this?