While standing may be hard on your feet, I'm inclined to believe it's really the extra weight that leads you to feeling like you just want to sit after you get off work. I worked a seated job, and with all my extra weight, all I wanted to do when I got home was to plop down and rest. I had to force myself to get out there and exercise, and keep forcing myself. I had to provide myself with ways to not get out of it so I couldn't think up excuses to get out of it. And eventually, I noticed I had to do that less and less.
Now, I actually enjoy doing things. I don't work anymore...SAHM right now. But I was still working after I lost the weight. And I found myself going out with a friend after work, or doing my grocery shopping some evenings rather than waiting for the weekend. It was like I couldn't sit still. I found myself looking for reasons to get up and move both during and after work.
Part of that was the weight loss, and part of it the energy obtained through exercise. So that even now, if I feel washed out some days and not wanting to exercise, those are days I'll usually push myself to do some kind of exercise. Because I know that once it's done, I'll have this huge resevoir of energy that builds up from the exercise itself. Then I can tackle other things rather than feeling washed out.