AFAIK, there is no online .hack based game. People do sometimes have seisures caused by video games, but it's a very limited segment of the population; nothing as far reaching as the 'Deadly Flash'.
Just a warning: They expect you to continue to play for a while before moving on to the next game. There is a several level difference between the monsters you're fighting at the end of the story on one game and the monsters you're fighting at the begining of the story on the next, and one of the games if you don't take measures to prevent it (read: ignore all e-mail), you'll be stuck underleveled with noone to help you out (one of the first missions is one of those missions where you can't contact anyone to go with you).
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