Photo: Videologia/Getty Images/iStockphoto

Have you ever been so stressed-out, so worked up and anxious and afraid, that you … fell asleep? Stephen, a 32-year-old travel agent in New York, says it happens to him all the time. “There are times, particularly when I have something really big going on, when I’ll become so incapacitated knowing I have a million different things to do that my body ends up saying, ‘You know what? Let’s just sleep,’” he tells me. “I’ll go and lie down and pretend that the rest of the world doesn’t exist. I just started calling them my ‘fear naps.’”

A few years ago, I had a Twitter conversation with someone who, like me, was afraid of flying. Unlike me, however, this person’s response to flight anxiety was to fall asleep before takeoff, and stay asleep until the plane had landed. As someone who’s spent many flights desperately clutching the armrests as if the force of my grip alone might keep the airplane aloft, this didn’t make much sense to me. (Nor did it seem particularly fair.) Why, if you were afraid for your life, or even just fairly stressed about it, would your body respond by falling asleep? As far as I knew, human beings react to the threat of danger with one of two possible responses: fight or flight. One or the other might be a smarter choice, depending on the situation at hand, but both options make sense as reflexive means of survival. But how could falling asleep help anyone?

According to Dr. Curtis Reisinger, clinical psychologist at Zucker Hillside Hospital, the classic “fight or flight” binary is oversimplified; there are actually a number of evolutionarily adaptive ways human beings might respond to stress or danger. “There’s also a freeze response — sort of like a deer in the headlights, they get stunned,” says Reisinger. “A similar one is flooding, where the person gets flooded with emotions. And then the other one is what’s called the fawn response, another F.” (I ask if this all-F naming convention was done on purpose, but he doesn’t know. He just realized it right now, too.) The fawn response refers to the inclination to cooperate or submit oneself to one’s threat or captor. And then there’s the final F: fatigue.

There are, of course, many forms of fatigue: There is physical fatigue, like what follows after you run a marathon (or so I’ve heard); there is cognitive fatigue, like what might follow an intensive several-day study session; and there is emotional fatigue, which Reisinger says happens a lot to nurses, physicians, and other professionals who work closely with sick and suffering people. Though the responses to these different forms of fatigue may vary — in the amount of time it takes to recuperate, or the specific form of tiredness one feels — there is one thing that unites them. “When you look at a psychophysiological level at all of these, one of the reasons that people sometimes get so wiped out and even fall asleep is that whenever you’re put up to a lot of mental tasks or physical tasks, it uses up glucose in the brain,” says Reisinger. “Glucose is essentially sugar, and it gives you the energy you need. My thinking on [the fear nap] is that the most likely culprit, if you will, is depleted amounts of glucose in the brain.”

No offense to Stephen, or anyone else who falls asleep when they’re anxious or afraid, but Reisinger points out that this response is not exactly unheard-of — it’s just that the people who do it are usually, ah, a little younger. “Sometimes with little kids and babies, when they get really stressed out, you know what they do? Fall asleep,” he says. Importantly, because children cannot themselves consent to being studied, much of our understanding of children’s relationship to stress and sleep is conjectural, and based off studies done on adults, says Reisinger — though it follows that children, with their limited stress-relief resources, are more likely to fall back on sleep. “I’ve had enough little kids in my house to know that sometimes if things are too stressful and they’re screaming and crying, they just zone-out after that. And that is akin to the metabolic exhaustion that goes along with glucose levels.” The brain requires immense amounts of energy, and is thus, says Reisinger, a big consumer of glucose. Taking a nap restores that depleted glucose in most cases (with the possible exception of those involving long, sustained periods of stress). And with that restored energy, we are more likely to be able to put our various challenges and stressors into perspective. This is also true of consuming something sweet, like lemonade, or a piece of candy, says Reisinger. So if you, like me, are someone who responds to stress by eating sweets, don’t go thinking you’re so much better than fear nappers — we are one and the same. Fear naps are simply less common.

Dr. Steven Feinsilver, the director of sleep medicine at Lenox Hill Hospital, tells me fear naps (or stress naps) are not something he hears about often, though there might be an easy explanation for that: “People come to me if they’re not sleeping well,” he says. “If they’re sleeping enough, and napping, they’re not coming to see me.”

Feinsilver says that while the fear nap may be a useful skill in high-stress but low-threat environments (like flying on an airplane, or watching a scary movie, or in a quiet conference room at work), it’s unlikely to work in times of true danger. “Most people, in the height of genuine fear, aren’t going to be able to just fall asleep,” he says. “And if they are, I worry about that.” Feinsilver and Reisinger alike point out that there is a line between the restorative stress nap and attempting to literally sleep one’s troubles away. “If they’re under so much duress and stress that they essentially just throw in the towel and give up, then that looks more like depression,” says Reisinger. Depression, of course, has many symptoms, of which oversleeping is only one (as is, for that matter, insomnia), so fear nappers needn’t necessarily worry. For the most part, for most people, more sleep is a good thing.

In Stephen’s case, fear naps do often alleviate some of that existential dread. “In the moment, it’s a really good way to take a step back. It’s somewhat meditative in that way,” he says. When it doesn’t work, it’s usually because he feels guilty for delaying the inevitable: “There are other times when I’ll wake up and it’ll come on that much worse, because in addition to the stuff I’m stressed about, I’m also mad at myself for being a degenerate.” But according to Feinsilver, you shouldn’t be too hard on yourself for something as essential — and productive! — as taking a nap.

“Sleep is very useful,” says Feinsilver. “It’s a much better way to shut things out than many of the other things people use, like alcohol. You can almost never get too much of it.” So while falling asleep may not be the best or most practical way to deal with actual, imminent danger, if you’re an adult with the somewhat rare ability to fall asleep when stressed, count yourself blessed. When the rest of us are out here frantically guzzling M&Ms, you are at peace, sleeping like a baby.