No matter what kind of work are doing you need to be sure that we take a break or some time out. You can wear a watch with an alarm or keep a timer on your desk. Set it to go off once an hour. When it beeps, stop your task, take a deep breath, and stretch any tight spots. Lack of movement creates fatigue, but brief breaks keep you clear-headed. It will not clear your mind but also it will give new perspective on what you do.