Mark R. Rosekind, Ph.D., is President and Chief Scientist of Alertness Solutions, a scientific consulting firm that works with corporations to maximize alertness, productivity and safety. He formerly led the Fatigue Countermeasures Program at the NASA Ames Research Center.

How sleep-deprived are we as a society?

Dr. Rosekind: We know from data that most people get probably about an hour and a half less sleep than they actually need, so even though we may physiologically need eight hours of sleep every single night, most of us are operating on maybe six and a half hours of sleep.

That's an issue because when you lose sleep it doesn't just disappear. You actually build what's called a cumulative sleep debt. You can think about it like a bank account. If you're getting an hour and a half less sleep than you need over five days of the work week, then you're going into the weekend basically seven-and-a-half hours in the red; it's as if you stayed up one full night going into the weekend.

What does that sleep debt mean to us on a daily basis?

Dr. Rosekind: Well, we know that getting about two hours less sleep than you need is enough to significantly reduce or even impair your performance and productivity the next day. So if you need eight hours and you're only getting six or less, then we know the next day you're going to pay for that. If you need eight hours of sleep and you got seven, you're only an hour in the red, it's not a big deal.

But over two nights it just became a big deal. If you're seven-and-a-half hours in the red by the end of the week, you should watch yourself driving home on that Friday afternoon. So we're individually paying a cost, but that also obviously puts people around us in our society at risk as well.

Can we buy back that sleep?

Dr. Rosekind: The good news is that you actually recover from sleep debt by sleeping deeper, not necessarily a lot longer. So typically when you're very tired you get more deep sleep when you do sleep, so it might only take you one to two nights to recover.