What do the Exxon Valdez, the space shuttle Challenger disaster, and your recent poor performance on you History (or Math, or Philosophy or whatever) exam have in common? No, it is not the fact that all were unmitigated disasters, but rather the fact that a lack of adequate sleep and consequent daytime sleepiness were definite "direct causes" in each of the first two disasters, and likely a major contributor to your own smaller scale disasters. Contrary to the portrayals by the media, it was not the Captain's being drunk that caused the Exxon Valdez to run aground and create one of the biggest oil spills and worst environmental disasters in history. Rather, because there were ice floes in the shipping channel as the supertanker left port, the Captain had ordered the ship to briefly leave the channel to avoid the ice and then steer back into the channel once they were clear of that hazard. The Captain had actually left the bridge and turned over command of the ship to the third mate. However, this individual, who had slept only 6 hours in the 48 prior to the ship's departure, forgot that the autopilot was on and didn't notice that the ship failed to turn back into the shipping lane when he ordered the helm to starboard. Once he did realize his error, the kind of information processing error that is typical of someone sleep deprived, it was too late!
According to pioneer sleep researcher Dr. William Dement, in his 1999 volume The Promise of Sleep, we live in a chronically fatigued society in which excessive daytime sleepiness is an unnoticed but potentially tragic reality of life. In surveys carried out by the National Sleep Foundation, 75% of adults said they experience daytime sleepiness and 34% said sleepiness interfered with their daytime activities. And being chronically sleep deprived is practically definitional of being a college student. In studies of college students at Stanford, the students exhibited such "pathological" levels of daytime sleepiness that they could not be distinguished from patients with narcolepsy, a sleep disorder characterized by nearly continual sleepiness and sudden daytime "sleep attacks." The college students were not in the early stages of narcolepsy. They were simply not getting enough sleep!
What the work of Dement and other sleep researchers has made clear over the last 30 years is that sleep is a basic and periodic biological drive, much like hunger. Just as hunger is our brain's way of signaling to us that we have gone for a period without food and are in need of fuel, sleepiness is the brain's way of telling us that we have been awake too long. In fact, our brains keeps an exact accounting of every hour we are awake, and in so doing are measuring our "sleep debt." As Dement says, "all wakefulness is sleep deprivation," and every night we attempt to pay down the debt. Although there are some small individual differences in what constitutes a person's "daily sleep requirement," and although there are some age-related differences in sleep need, "generally people need to sleep about one hour for every two hours awake, which means that most need around eight hours of sleep a night." One of the breakthrough moments in the history of sleep research occurred when Dement and colleagues found an objective way to measure daytime sleepiness, the MSLT, the "Multiple Sleep Latency Test." By taking repeated measures of how long it takes individuals to fall asleep during the day, researchers have not only quantified daytime sleepiness but have correlated it in a linear way to the number of hours of sleep debt the individual has accumulated. And they have found that accumulated sleep debt is correlated with dramatic decreases in performance, mood, motivation, energy and sense of well-being. People often automatically begin to suspect insomnia as a symptom of depression, but Dement's research documents that the causal vector can move the other way, that lack of sleep may significantly depress our mood. So, if our need for sleep is like our need for food, we are living in a society of sleep anorexics!
You may protest that even though you get far less than 8 hours of sleep per night, most days you feel fine, especially at night! Dement clarifies that "because the alertness-sleepiness continuum is actually a complex function of sleep debt, biological alerting, and environmental stimulation, we are generally very bad judges of our sleep tendency." Opposing our internal drive for sleep there is a biological clock, a kind of internal pacemaker, that twice a day, in the morning and again in late afternoon and early evening (and later for most adolescents), stimulates us to feel more awake even though we may have some accumulated sleep debt. This "clock-dependent alerting" explains a number of variations in our level of wakefulness-everything from "jet lag" to the late night burst of energy, to the early afternoon "slump" that so many of us feel (and which is, contrary to popular belief, not due to the effects of lunch).
Dement elucidates a full spectrum of negative consequences of insufficient sleep, but at the far end of the spectrum his mantra and main take-home message is that driving while drowsy is supremely dangerous. Whenever you feel drowsy while driving you should regard that as a severe red flag that you need to pull over and get off the road and take a nap immediately. Sleep is not something that we gradually slip into, but rather its onset is sudden, as if the brain flips a switch and we are out. Further, Dement presents convincing evidence that in many driving fatalities that are attributed to alcohol, "the real culprit, or at least a co-conspirator, is often sleep deprivation." Alcohol unmasks sleep debt, and even a small amount of alcohol, combined with a large sleep debt, can create a "fatal fatigue." Particularly as we head into final exams, and the approaching holiday season, this information can be life-saving if you are mindful of it.
In order to assess your own sleep debt, ask yourself the following questions: How sleepy do I feel during the day? How often do I yawn or actually fall asleep in class or doing homework? How frequently do you want to nap or feel you need some coffee? When you take a daytime nap, if it takes you less than 5 minutes to fall asleep, you are "pathologically sleepy"; less than "10 minutes and you are "borderline." Dement asserts, and I would agree, that we cannot overstate the dangers of unintended sleep episodes and daytime drowsiness. On the other hand, people who have taken control of managing sleep in their lives and lowered their sleep debt gain a new sense of zest and well-being. You can too!