Learn to distinguish a job rut from a dip (an ultradian dip, that is).
"We cycle through the ultradian stages every 90 to 120 minutes. Practically, this means that for about an hour and a half to two hours after rising in the morning, we feel particularly vigorous and focused. At the end of that interval, however we experience a 20-minute period of fatigue, lethargy and difficulty concentrating. This is the 'ultradian dip.' At these times we need to relax or switch our activity to something different—for example, take a 20-minute power nap, a walk outdoors, meditate, listen to music, read a chapter of a novel or gossip with colleagues (but not about work). In a study conducted with employees of 12 Wachovia banks in New Jersey, those who were prompted to renew their energies in these ways reported being more engaged and satisfied with their work, showed improved relationships with customers and produced 13 percent more revenue from loans than did a control group. Think back to the last time you felt particularly dissatisfied or stressed at work. It's highly probable that you were weathering one of those 20-minute ultradian dips. This doesn't mean, of course, that those feelings of disaffection or vexation aren't symptomatic of a real problem, but it means that we should be cautious about overinterpreting them."
From The The Myths of Happiness: What Should Make You Happy, but Doesn’t, What Shouldn’t Make You Happy, but Does (The Penguin Press) by Sonja Lyubomirsky