Well I didn't have any naps, so that isn't it.

I didn't eat any candy that day. But even if I had, I've eaten huge amounts of candy before and nothing bad has ever happened.

I suppose it could be dietary, but I've had a lot of dietary and digestive type problems and this wasn't anything like that. Plus, again, I didn't eat anything that I haven't eaten before and been fine.

The motion sickness thing does show promise though. I've thought that before, especially since it happens on the bus a lot. It also happens if I play a video game for too long, or if I'm on the computer for a long time like I was that day. But it's never been as serious as it was that day, so I think that even if motion sickness was part of it there must have been something else to it as well.

I've been reading some stuff about migraines. A lot of it seems like it matches up. "Migraine headaches are usually characterized by severe pain on one or both sides of the head." "Migraines are often accompanied by photophobia (hypersensitivity to light), phonophobia (hypersensitivity to sound) and nausea."

It talks about the phases:
Prodrome phase "may consist of altered mood, irritability, depression or euphoria, fatigue, yawning, excessive sleepiness, craving for certain food (e.g., chocolate), stiff muscles (especially in the neck), constipation or diarrhea, increased urination, and other vegetative symptoms."
I'd say that matches up because around the time this happens I usually feel really bad and depressed, and don't want to move or speak.
The aura phase is basically when all your senses are screwed up, like for me when I can't look at things or hear things without pain or nausea.
The pain phase is pretty obvious, it also fits in how it says that activity can make it worse, which is true for me. If I do anything other than remain in one position with my eyes closed unmoving, it intensifies.
Postdrome phase, "some people feel unusually refreshed or euphoric after an attack", that describes what happened that day. "The patient may feel tired, "washed out", irritable, listless and may have impaired concentration, scalp tenderness or mood changes." Aside from the "scalp tenderness", that describes what happened the next day, and what usually happens on the less serious occasions.

So now that I look at it, I've probably just been having migraines for most of my life and not known it. I don't know what made it so bad that time, probably a combination of things including what I ate, extended computer time, maybe even weather. I guess if I can figure out exactly what it was I'll have a better chance of being able to stop it. Unless it's a tumor, which just now occured to me. I'm kind of hoping it isn't though.