"It's only one hour," said David Dinges, a sleep researcher at the University of Pennsylvania and editor of the journal Sleep. "But it's acute."
The sudden shift of circadian phase disturbs the body's natural rhythms, said Dinges.
"Our brain contains this old biology that is consistent with the earth," he said, explaining that we are wired to rise with the sun and sleep after dark. "But the relentless part of our brain keeps pushing us to go everywhere and do everything."
Theoretically, in the fall we gain an hour of sleep, which ought to make us more rested and happier.
"Unfortunately, people tend to use that extra hour for waking activity," said Christopher Barnes, assistant professor of management at the University of Washington.
Barnes' research shows that although people are sensitive to any changes in shut-eye patterns, the effects are worse in spring when the hour is stolen.
On "Sleepy Monday," the day after an hour is lost, people suffer more workplace injuries.
"Mining injuries go up by almost 6 percent and the severity of injuries go up by 60 percent," he said. Other studies show that after clock changes, traffic accidents increase and people are more prone to heart attacks.
Furthermore, Barnes said, workers who manage to reach the office alive and well are more likely to waste time "cyberloafing."
For decades, research consistently has found that traffic accidents increase after the clocks spring forward. There is some disagreement, however, about the fender-bending effects of gaining the extra hour in the fall.
One study looking at alcohol-related fatal traffic crashes in New Mexico found a significant increase not only on the Monday after, but for the entire week after the changes to and from daylight saving time.
Others have detected a brighter side, so to speak, and contended that there are fewer car accidents when people get back on the road after the clock returns to standard time.
Stanley Coren, a psychologist at the University of British Columbia, found that while traffic accidents rose 8 percent the day after daylight saving time went into effect, it dropped by the same percent the day after it ends.
Several researchers have concluded that the biannual switch flipping of time creates mass "sleep desynchronosis."
Studies of airline pilots show, "that even one hour of jet lag impairs hand-eye coordination, cognitive ability, and memory," said Mark Kamstra of York University in Toronto. "And daylight saving time effectively puts most of the continent on jet lag."
When Benjamin Franklin first conceived of daylight saving to conserve energy, he could not have dreamed of the high-tech fallout. Every time the clocks change, medical devices, such as pacemakers and defibrillators with sleep modes and glucose monitors for diabetics, have to be adjusted.
Aside from the losses in productivity, the medical costs and damaged machinery, the national wrinkle in time inflicts another weird economic wound.
With the caveat that, "it is difficult to ferret out these things directly," Kamstra said, "but on the Monday following the daylight saving time changes, the stock market shows lower than average returns."
In a 2000 study in the American Economic Review, Kamstra and his colleagues reported that the Monday after losing and gaining that precious hour, stocks drop about half a percent. "Which is a pretty big number for a single day," he said, reporting that the losses amount to about $30 billion.
Kamstra said his is not to reason why, but he is willing to venture a guess.
"Think of any weekend when you really disturb your sleep patterns," he said. "People emotionally are less inclined to take risks. . . you're basically just a little more wobbly."
His work has been challenged, he said. "It's statistics. People are skeptical."
Still, he and his wife, Lisa Kramer, who co-authored the study, have so much faith in the study that they staked (part) of their own fortune on it.
"We have traded on that Monday," Kamstra said. "And two out of three times, we made money."