I found similar outcomes. I just did some math and I am standing up nearly 14 hours per day. I eat all my meals standing up now too. The only time I sit down is when I am playing games, driving (rare these days), or getting ready to go to bed.

As mentioned by other comments in this thread, there are issues with standing completely still all day. I find myself shifting weight between my legs throughout the day, and finding occassional excuses to walk in circles or visit the whiteboard.

After a while you don't even process it as some sort of inconvenience. Sitting down actually drives me nuts now. It feels "wrong" for some reason. I have no trouble getting to sleep at night though.