Y: Today, on a Moment of Science, we're conducting an experiment on sleep deprivation. On my right, we have my friend Bob, who hasn't slept in eighty-eight hours straight! Bob? Bob? Okay, so he's pretty unresponsive. And on my left, we have Don, who has been restricted to no more than four hours of sleep a night for the past two weeks. How are you feeling, Don?
D: (YAWNS) Well, I'm a little tired, Yael, but not as tired as Bob over there, who I think is drooling.
Y: If you've ever relied on a doctor or an airplane pilot, then you know there's a lot at stake over whether Don is telling the truth about how tired he feels.
D: Of course I'm telling the truth. I feel fine (YAWNS).
Y: Well, you might think you feel fine, but I have in front of me the result of the cognitive performance tests both you and Bob over here took earlier today. And guess what?! Don! Don!
D: Huh? What?
Y: These cognitive performance tests show that you and Bob are having equal trouble performing some pretty basic tasks.
D: But Bob hasn't slept in three days!
Y: Exactly. So that means that even missing only a couple of hours of sleep a night really adds up if you do it every night. In other words, sleep debt is cumulative, and right now, you have no more business going out there and driving a car than Bob does. What's more, you're so tired right now that you can't even properly evaluate how tired you are, which makes your sleep debt even more dangerous.
D: Guess I better catch up on some Zs!
Y: Looks like Bob's beaten you to it.