If you came to and were basically immediately "with it" it probably wasn't a seizure (aside of the twitching). It's the post seizure period of confusion that generally decides whether it was a seizure or no.
Low blood sugar is notorious for causing out of the blue fainting, especially when it's combined with lack of sleep, physical activity, alcohol or illicit drug consumption within the past 24 (not saying you were, just listing the common stuff), heat stress, dehydration.
You're heart will pound like mad when your blood pressure goes down, if your blood pressure dropped when you stood up, combined with the low blood sugar ... well, you rebooted your brain
I wish you the best of luck in this matter and in finding out what the hell happened and why. I think not knowing the what's and why's is the most irritating part. I still never got a satisfactory answer as to the cause of the tumor I was diagnosed with last year... three ENT surgeons and over half a dozen doctors with nothing but speculation.