Take a day off once in a while. It won't hurt anyone and you will feel better for it. If your day job is anything like mine...all the work will still be waiting for you when you go back. So don't feel guilty! If you don't have a day job and you write full time (I am beating down the extreme jealousy) then take a break and spend some time outside. Recharge those writery batteries. Sometimes a little time away is all you need to get past any blockage or figure out that twist you threw in and now don't know how to resolve.