Q. Every day after lunch, you find yourself overcome by drowsiness, and you can’t get any work done because you just want to crawl under your desk and go to sleep. Why does this happen?
A. This universal phenomenon, known as the “post-lunch dip,” represents a collision of biology and economics.
It is entirely natural for humans to want to go to sleep about seven hours after they have awakened. But as the internal rhythms of the body call out for rest, the efficiency of the modern workplace demands continued exertion.
Q. What is happening in the body that it craves rest after lunch?
A. First, the 24-hour cycle of the body, or its circadian rhythm, is naturally in a resting phase at this time. In the afternoon, it happens to converge with another physiological cycle — known as homeostatic — that measures the amount of time spent awake and that is also pushing for a rest.
Add the effects of food, which can also induce drowsiness, and an overpowering desire to sleep may result.
Q. Do all people experience the post-lunch dip?
A. The effect may be natural, but “not everyone experiences it with equal intensity,” said David F. Dinges, a professor and sleep scientist at the University of Pennsylvania
School of Medicine.
A few people say they don’t feel the dip at all, while others — about 15 percent to 20 percent of the population, he estimates — are “closet nappers.” These are the ones who steal into empty rooms or their parked cars, or fall asleep at their desks, because they can’t fight off the urge to close their eyes.
Often, these people are ashamed of their behavior because it is associated with laziness, Dr. Dinges said. But by giving in to the urge, they are actually improving the quality of their work.
Q. Can being drowsy at work affect productivity and quality?
A. Yes. A study of drivers found that more car accidents occur during the afternoon dip than at noon or 7 p.m., Dr. Dinges said.
Few studies have been done on drowsiness in the workplace, but it seems likely that more errors in judgment are also occurring in offices, on factory floors and in other work environments at this time.
If possible, workers who are unable to take a nap should try to perform more mundane tasks during the dip, and save projects that require the greatest accuracy, mental acuity and creativity for other times of the day, said Fred W. Turek, a biology professor and director of the Center for Sleep and Circadian
Biology at Northwestern University