I knew a few people who got "lost in the game" when I played RPGs.
I knew three guys from my high school gaming days who got trapped in the game just as bad as Tom Hanks. In reality, it wasn't as dramatic as Hanks' character. These guys didn't actually believe they were living in a fantasy world, but they were trapped in it just the same.
While most of us in the gaming world at our school grew up and either moved on from gaming or kept gaming as an occasional pastime, these guys continued to be just as involved as they were at the height of their teen RPG obsession.
They either lived in their parents' homes well (decades) into adulthood, or lived in rooming houses or bachelor apartments on welfare or disability or perhaps a minimum wage joe-job now and then. Every spare penny they had went into gaming. They had no social lives outside playing RPGs and attending cons. They didn't really play with a group of actual friends, because they had none, but with people at gaming stores and clubs who were more or less strangers away from the game table. Romantic partners were totally out of the question for these dudes.
When you spoke to them, they would never, ever talk about their real lives, but instead give you elaborate descriptions of what amazing deeds their RPG characters were up to. Whenever I bumped into one of these guys and saw how obsessed and lost he was, I would get this really sad, sick feeling in my stomach.
2 of them are dead from health issues now, and I have no idea what the other guy is up to.