Integrating that kind of psychological element into the game wouldn't work, and would at best be cheesy. The physical health of the character, his needs for food, water, heat, these are inescapable biological necessities that are both realistic and within game confines. What I mean by game confines is that, though realism is an aim of this video game, it is, at the end of the day, a game. It's a technologically advanced form of chess, with rules to enhance the experience; ultimately, however, the psychology of the character, avatar, (whatever you want to call it), must be the psychology of the person controlling it. Once you begin taking the mind game away from the players and instituting a game limitation to it, then an integral piece of the game is lost. Now, there are instances of games that use this psychological 'hinge' as a game mechanic. Eternal Darkness and Amnesia come to mind. But in the case of these two games, there is no competition between players, it is a man/woman versus the enviroment (a scary house, malevolent forces, etc) it's easier to integrate those elements into a game of that type. But even then, the experience must be limited to the scripted experience that the developers want you to have. It's a haunted house on their terms. For a game like Day Z, an open world of competitive play, it will not work.