I remember reading about something very similar a few years ago... I can't remember what game they were playing, but some Asian guy died in an internet cafe during a gaming event of some kind.
I also remember hearing about another story of a boy in the UK dying from a blood clot because he had basically been sat for so long playing on his Xbox. In fact, I just did a search on Google and found the article... read it here.
Pretty crazy. I don't think my eyes would allow me to play for that long, never mind anything else!
If you sit for to long blood clots will form. I have always heard you should get up and move around a little if you are going to be in one place for awhile. This can be a big issue on long plane flights as well.