XD
Without going outside and getting a good taste of nature, our immune system wouldn't have encountered all the bacteria needed for the white blood cells to create memory cells to fight off the invading pathogens. Our immune system wouldn't really be that active, and that's not very could now, is it? True, it'll weaken eventually as you get much, much older, but this can affect it negatively because of a lack of outside activity...or any physical activity at all.
Source: A* Science student. (Seriously though, As and sometimes A*s)
Then explain all those people who died of a lack of nutrients because they were too sucked into video games. Our brain doesn't control us, it just keeps us alive. It can't do that very well without all 7 essential nutrients. This device will probably be far more powerful and addictive than just a computer screen. You'll be sucked into the Virtual Reality and probably wouldn't want to return that easily.
That's what I'm thinking. There could be a little time on the side that tells you when you should take a break. To avoid getting too addicted, there could be an option to shut down the whole thing after a certain period of time. I'm sure the instructions manual will come with a suitable time to spend on this.