I'm usually not one to advocate the U.S. legal system for anything, but I'll make an exception today for them. Take this company to court; at worst-case scenario, you'll get a settlement for lost wages plus damages and court/lawyer fees. I am making the assumption that you at some point during your employment listed your medical condition in writing (which is almost irrefutable).

You can't always tell when you're low, sometimes it happens really suddenly. Even is the OP had told the coworkers, maybe they didn't remember or they panicked. And I'm really wondering how it looked like you were sleeping. It's a seizure, usually people don't twitch or scream when they're asleep.

Not all people who experience seizures experience them in the same way. Some people have grand mal seizures with the twitching and thrashing, some people have complex partial seizures where they will get up and try to walk away (even when they are in a car on the high way. nice going, sister mine). Some people just blink, and some people pass out. I've only experienced one person's variety of seizure (epilepsy induced, not diabetes, so dubiously valid) and seizures ALWAYS made her sleepy. So it probably was a genuine seizure, it just didn't look like the kind you see on TV/the kind you yourself may have experienced.