Ah I have seen this a few times before, one time when I was 19 (Legal drinking age here), my friends and I were having a few alcoholic drinks and rolling dice to see what our saves were against becoming intoxicated. Things like this are okay but I have seen some people obsess very hard over Dungeons & Dragons. One friend I had was bad for this, he wanted to play every second of every day and would call me for hours explaining characters he optimized for 1-20th level, he would put so much time into it that it was effecting his personal life and ability to work / function, he would stay up all night just to perfect muti-class builds that bared no weakness. This was around the time I stopped hanging around him but I did hear a year or two later that he was diagnosed with schizophrenia and admitted to the psyche-ward.
If someone has mental issues then it does not matter which game they play because their problems go like totally outside of the game, really it has nothing to do with the game.
As mentioned by others, a little bit of commitment or even thinking up stats for people is harmless. As long as you don't neglect your responsibilities, and have the ability to focus on other things, you're fine. Try avoiding mentioning the game in conversations with random people, there are so many other interesting things to talk about, and you're missing out on a lot of fun if you're just thinking/talking about a game all the time.
Do people really get so addicted that they they think they ARE the characters they're playing? That is so weird.
I have seen it many times. My son in his first year of college had a roommate who got so into World of Warcraft that he tried biting others who came near him as he would do that with his character in World of Warcraft. I guess he could not tell reality from fantasy anymore.
As far as addiction to Dungeons & Dragons I am sure that I do not want to overcome it.