The heart ticks to a circadian rhythm, too, says Martin Young, PhD, a cardiovascular scientist at the University of Alabama at Birmingham. In the wee hours before dawn, the heart is slowly preparing itself for the strain of starting the day. "But when your natural rhythm is off, that process doesn't work the way it's supposed to," he says, "which means waking comes as more of a shock to your system." This may partially explain why, in the days following the start of daylight saving time each spring, before our bodies recover that "lost" hour of sleep, the rate of heart attacks shoots up by about 5 percent.

After-hours brightness could even affect your weight. In a study published in October, researchers at Ohio State University exposed one group of mice to a dim light at night, while another group was allowed to experience a standard day-night cycle. Over two months, the first group gained 50 percent more weight than the second group—even though both ate the same amount of food and had similar activity levels. The only difference was that the first group began eating at unnatural times—when their digestive systems were not keyed to metabolize food.

The brain, too, runs on a timetable, and evidence indicates that changes in its natural rhythm can lead to anxiety, cognitive decline, and depression, says Alan Rosenwasser, PhD, a psychology professor at the University of Maine in Orono. Depression and an out-of-whack body clock are an especially dangerous combination because the disease can in turn cause further disturbance in a person's rhythm (so much so that antidepressants alone are capable of resetting the body's clock). Rosenwasser has also discovered a connection between the day-night cycle and addiction: Lab mice forced off a normal schedule actually experience an increased craving for alcohol.

We are just beginning to understand the effects of our extended days, but it's becoming more and more clear that our habit of cheating darkness may lead to a rude awakening. The good news is that it's possible to nudge yourself back to a healthy rhythm.

As for Tamika Handy, she has begun finding ways to whittle down her days and lengthen her nights. By focusing on the tasks she absolutely must accomplish in a 24-hour period—and pruning out the rest—she has shortened her daily to-do list to a manageable length. "When my family is getting ready for bed, I'm no longer running around feeling guilty for all the things I haven't yet accomplished," she says. That sense of satisfaction allows her to relax a little bit. Then, at about 9 P.M., she turns off the television, shuts down the computer, and relaxes with a good book. At 10 P.M., it's lights out.

Next: Follow these simple steps to fix your sleep schedule