This kind of stuff can be quite serious. My dad was almost paralyzed when his back went out in a bad way a few years back, from sitting for too many hours at a stretch at his computer for a number of years. He ended up out of work for something like six months or so. Fortunately he had oodles of vacation time saved up, and so combined with his sick leave, was able to have full pay for the entire time.
I know that most of us that browse these forums sit at a computer for many hours at a time, so this should definitely apply to us. It's rather important to be aware of the dangers of not moving, and change your habits before ending up with a debilitating injury.