Today's task: Get up from your desk more often.
Why: I'm sure you've heard "sitting is the new smoking." It has all these lethal effects on your body that sneak up on you over time. What I've seen is when people get off their butts - by installing a stand-up desk, taking frequent walks around the office, standing during phone calls, etc. - they have more energy and they FEEL better. Their backs don't hurt, their hips aren't as tight, and they can fall asleep easier at night.
To make this a permanent solution: The best solution is to invest in a desk that can be used for standing or sitting - because going from 8 hours of sitting to 8 hours of straight standing causes its own problems. Find a good balance of sitting and standing. If you can't invest in a standing desk, get up and shake your legs out every half hour, stand while you're taking a phone call, stand during lunch, and/or make your co-workers think you have a small bladder by walking to the bathroom and back in between office tasks. When they ask what the heck you're doing, get them moving, too!