Recently, I worked at another office to make use of their equipment and of my father. I set up at one of these really cool work benches they have. The benches are tall enough to stand and use.
For the entire week, I worked without sitting down. I wrote programs standing, played around with circuitry while standing and even read manuals while standing.
When I came back to my office, I continued my life of sitting to work. I noticed that, compared to the previous week at the other office, I was sluggish, having troubles staying awake, and having troubles focusing. I tried several things I thought would help, none of which did. I was already getting plenty of sleep. My high tolerance to caffeine rendered coffee useless.
Eventually, I realized what was happening. I live a pretty active lifestyle, and the only time I sit down in a quiet area is to sleep. When I sat down in the comfy chair in my quiet office, my body saw this as an opportunity to sleep.
I took a rubber tote, put it on top of my desk, put my computer on top of that, and now stand while I work. The results have been remarkable! Sometimes my feet hurt at the end of the day, but that is a price I am willing to pay. I stand while I work, not for the posture and back pain relief benefits that everyone keeps screaming about, but because it makes me more productive.