The truth may be that there are some underlying issues affecting your overall mental clarity. Your body’s ability to adapt to stress and fatigue while operating at a productive level begins to deteriorate after time. For some people, this is a gradual change, and for others, it may feel like it came about all of a sudden. Those moments of rapid change may lead you to believe that you are feeling tired or having a rough day at work, when in reality, it has to do with much more than that.