Last weekend I had the luxury of being able to spend a couple of long sessions on composing, always my favourite type of session. Saturday night, after 6 hours of producing I decided to take a break before I came back and continued working on my project. I was amazed at the difference that taking a break made. My ears had become extremely fatigued, and I couldnt hear the relative levels of each of the instruments that I was mixing. A short half hour break completely helped reset my ears. Not only this but it allowed me to stretch a bit, get the circulation going again and loosen up my back muscles, which let's face it can get pretty stiff sitting in an office chair for an extended period of time. I think this is an important point to make, i'd previously looked at taking a break as lost time, however it's actually something that increases prodictivity rather than decreasing it.
In addition to the above, getting your mind off whatever the problem it is that you are tackling at that point in time can have it's own benefits. I've read many anecdotes about creativity where the answer to the problem came in a momnet of relaxation like when you're in a warm shower. Think of when you're looking for a word or a name that you can't remember. When you're trying to force it, you just can't come up with the information you're looking for. Later on when the moment has passed and you are more relaxed, focusing on other things, the answer comes to you. It can be the same with music, whether it's a mix problem you are dealing with or a creative problem, give your mind time to wander and you may be surprised at the results. In short, there is a very good reason top companies around the world like to create relaxed and comfortable working conditions, in that it fosters innovation. Are you taking regular breaks, and are you comfortable at your workstation or are you forcing yourself to work despite your conditions? If you arent taking breaks, you may want to consider doing so to boost your productivity. Just don't let scheduled breaks derail you from the task at hand, I know some people find it hard to get back to work after a short break.