Yet even that number, which emphasizes the physical and medical consequences of inadequate sleep, omits the biggest potential impact on the G.D.P. Most of today’s workers rely on their mental and social skills. And if those workers don’t get enough sleep, their lethargy, crankiness and poor decision-making will hurt the economy in assorted and significant ways.

For example, one study has shown that “cyberloafing” — wasting time on the web — increases on the day after the start of daylight saving time, when people are short an hour of sleep. Other research shows how cognitive performance deteriorates when sleep is inadequate: We have less capacity to remember, to learn or to be creative, and we become less optimistic and less sociable. And these consequences aren’t reserved for extreme sleep loss: Studies show that two weeks of sleeping only six hours a night can have the same impact as one or two nights of total sleep deprivation.

There is an odd divide here. Ask why one person had an unproductive day at work, and lack of sleep often seems an obvious answer. But ask why national productivity has fallen, and reduced sleep can appear to be a frivolous answer. Yet what is total output but the sum of all individuals’ work?

Sleep deserves serious study by behavioral economists for another important reason. Some struggle with medical issues — like insomnia — that make sleep hard. But for many of us, the quantity and quality of sleep come down to a matter of choice. Still, only a few enterprising economists have looked closely at this, and generally those have assumed that we choose our hours of sleep optimally. The idea is that we thoughtfully trade the use of an hour of sleep for an hour spent doing something else. But it is worth questioning the assumption that these are rational and optimal choices. Judge for yourself. Was watching that extra episode of “Game of Thrones” last night worth the sluggishness you’re feeling right now?

We also need to ask another question: Why do we neglect our sleep? It’s not as if the ill effects of fatigue are a surprise. If for no reason other than self-interest, we are vigilant about our children’s sleep, so it’s hard to understand why we are so cavalier about our own. This puzzle is even more pointed because the benefits of sleep are immediate. Eat better or work out more, and you’ll see the benefits weeks, months or years down the road. Sleep more and you’ll see the benefits tomorrow.