Seizures from video games are more common than people realize. They can happen when nobody knows they've happened. Seizures often don't look like what you'd expect, so anybody nearby might not notice. And somebody who doesn't know what it feels like to have a seizure might notice something odd--or might not, since their consciousness might be impaired--but have no idea they've just had a seizure. So as strange as it might seem, seizures can be happening totally unnoticed.
My daughter had subtle seizures every day for a long time while playing Gaia and other stuff, and nobody could figure out what was wrong. She usually played alone, but even if you're right there when she has these, you can't see when they happen. She never had seizures before that we were aware of, so we had no idea it was even a possibility. All the seizures made her tired, unable to focus, generally "out of it," unable to remember things. Doctors were puzzled. It was horrible.
Also, the tests done with strobe lights to detect whether you are photosensitive are not reliable. For one thing, they expose you to a strobe light, which is not the same as exposure to video game graphics, and for another, they use EEG--which is very inexact (doctors tend not to volunteer this information but there's plenty of research about it).
more info: www.videogameseizures.org (full disclosure--my website)
