Great post. I, myself, have a hard time when it comes to working too much. And at times, I do see that too much time spent working on something during a long period of time is not effective at all. I also feel that guilt when I finally submit an take a break. Personally, I would stay away from naps (and the Internet), and try to do something else like going outside or driving into the city and relaxing at a cafe with a cup of tea –all this for not too long, in order to regain my strength and get back to work. Though I tend to take my work wherever I may be, little breaks do wonders.