I also work nights and until recently was working part time for several months. I got out of the exercise habit when I moved, but before that, I had gotten very good about it. I started by doing an exercise video, Walk Away the Pounds. It's a series, but the first, simplest one is only 15 minutes. I'd tell myself if I can't even get off my butt for 15 minutes, then I'm REALLY pathetic. Pretty soon I was doing the tape twice a day instead. And then I moved on to the 30-minute tape.