Revisiting the status of sleep awareness 5 years after the founding of Sleep Review.

 I wrote a guest editorial which was published in Sleep Review in 2000. I believed at the time, and still do, that its message and recommendations are of utmost importance to everyone on the planet. For this reason, the editors have allowed me to retain much of the original 2000 editorial in the following text.

In the course of dealing with the many public policy and safety issues involving sleep, sleep deprivation, and sleep disorders, it has become clear to me that the number one sleep-related problem for society is sleep debt. Furthermore, the imprecise language with which we relate daytime feelings to varied nighttime sleep amounts hampers public awareness and action.

Before attempting to justify these assertions, the term “sleep debt” should be clearly understood. Each of us has a specific sleep requirement, an amount that we must obtain each night to maintain constant functioning. All amounts less than this constitute lost sleep, and the size of our sleep debt is the total of all nights of lost sleep.

Sleep Debt and Associated Problems
Sleep debt poses a threat largely because it is invisible. Few adults, adolescents, and children clearly understand that lost sleep relentlessly accumulates as debt. People are usually surprised when an overwhelming tendency to fall asleep overtakes them in soporific situations (for example, behind the wheel of their car). Moreover, few countries understand the sleep disorders associated with “excessive daytime sleepiness.”

Second, the vast majority of adolescents and adults carry a sleep debt of varying size and are chronically tired and sleepy. In a study of several hundred individuals who should have represented the most alert segment of the population, Levine et al1 found that more than 50% of young adults had a Multiple Sleep Latency Test (MSLT) score in the sleepy range of >10.

Third, our understanding of sleep debt is muddled with misattributions and erroneous beliefs. Many people seem to be somewhat confused about when they are fatigued versus when they are sleepy, and when they are not fatigued or not sleepy. In other words, people need to be more in touch with their feelings.

I have chosen to make this third issue and its role in our sleepy society the focus of the following editorial remarks.

The Semantics of Sleep: Sleepiness/Drowsiness vs Tiredness
The number one complaint among college students is “tiredness.” Analysis of survey data administered to more than 10,000 undergraduates at several universities and 2,000 high school students has yielded several important results:

  • college students and high school students feel tired more often during the day than they feel sleepy, and feel tired on more days per week than they feel sleepy.
  • the majority of respondents feel that tiredness is not the same as sleepiness, and that tiredness has a different cause. In my opinion, the most impressive example of confusion about tiredness and sleepiness is captured by the statement, “I’m too tired to fall asleep.” In the college population, this misattribution is commonplace because students do not equate tiredness with being sleep deprived and they are mainly unaware that strong clock-dependent alerting in the late evening (also  called the “forbidden zone” by some) can prevent falling asleep. Thus, the very sleep-deprived, tired student tries to sleep and cannot, and erroneously labels this situation as being “too tired to fall sleep.”
  • the words “sleepiness” and “drowsiness” mean the same thing to about two thirds of the students, but when they are not regarded as equal, about half of the remaining third say drowsiness is more intense and closer to sleep.
  • when asked to select the physical signs of sleepiness or drowsiness, the great majority (approximately 80-90%) select symptoms involving the eyes (“heavy eyelids,”  “can’t keep my eyes open,” “can’t focus,” and “eyes burn.”)

Because high school students and college students (and possibly all other adults) do not attribute the feeling of tiredness to chronic partial sleep deprivation, they inevitably underestimate their personal sleep requirement and undervalue the importance of sleep debt in regard to subjective alertness.

The Subjective Consequences of Sleep Debt
Those of us who are interested in the sleep-related determinants of daytime function justifiably regard the development of the MSLT as a major scientific advance.2 This objective measure of waking sleep tendency has shown a satisfyingly predictable relation to daily amounts of sleep over time, which, in turn, has allowed us to quantify the dimension of waking alertness/sleepiness and its nocturnal determinants. Dealing with the subjective side of the alertness/sleepiness coin has not been nearly as satisfactory. Correlation of subjective data such as the Stanford Sleepiness Scale (SSS) with objective data like that of the MSLT is often poor.3 One explanation for the discrepancy could be that the language used to make scale levels equidistant is somewhat arbitrary and possibly a little arcane to some individuals.

Although evaluating subjective sleepiness in research projects has not been totally unproductive, I believe there is a huge problem with communication surrounding levels of sleepiness/alertness with patients, health professionals, and the general public. MSLT scores have become extremely meaningful to sleep researchers, and a range of assumptions about individuals with a certain score can be confidently made. Quite frankly, I have very little confidence in using only SSS ratings to gauge sleep deprivation.

Daytime Consequences
Ever since Mary Carskadon and I carried out our first study of partial sleep restriction in the Stanford Summer Sleep Camp and showed that daytime consequences accumulate,5 I have exhorted students to get more sleep with only marginal success. More recently, I have introduced a project for extra credit in my Stanford University undergraduate course, Sleep and Dreams, which requires students to lower their sleep debt by getting as much extra sleep as possible. As expected, students who are able to obtain large amounts of extra sleep no longer feel sleepy in the daytime. A much more important result, however, is that they no longer feel tired! Furthermore, if these same students, for whatever reason, stop obtaining adequate sleep, they soon start feeling tired again. From this, we have concluded that the sole cause of “feeling tired all the time” in healthy young adults is a sizable sleep debt.

From all of this, we may conclude that our commonplace English language is deficient when it comes to expressing the subjective nuances of sleep deprivation. Recognizing this, I have recommended elsewhere6 that we should focus on defining three major levels of subjective waking alertness. One level is feeling sleepy or drowsy. As indicated earlier, most people regard the terms sleepy and drowsy as synonymous. The onset of the sleepy/drowsy state or level is defined as the moment of the first awareness that the eyelids feel heavy and a conscious effort is required to keep them open and to stay attentive. The second level refers to the period immediately prior to the onset of the drowsy level, when people are definitely not at peak alertness. They are much more likely to say they are feeling tired, fatigued, lethargic, or unmotivated. The third level is peak alertness and unambiguously not tired. The important advantage of precisely distinguishing these three subjective states is as follows: we have defined a detectable internal warning of impending disaster—a signal that absolutely requires a response. Drowsiness is red alert. Get off the road. Get out of harm’s way. Do it now!

As the field of sleep research and sleep medicine has become more involved with performance and safety, disseminating knowledge to the general public has become much more important and still greatly needs refinement. In 1990, the National Commission on Sleep Disorders Research launched a study that included interviews with 602 truck drivers and overnight testing of a subset of 200. It is quite certain that most of these drivers carried large sleep debts both because of inadequate amounts of sleep and because the majority were found to have obstructive sleep apnea. However, for the most part respondents denied having any serious problems with fatigue and sleepiness.

One result from the survey was profoundly surprising. When probed about the triggers that lead truckers to stop driving, 82% stated that they got off the road only after they fell asleep. The most common responses were “My head drops and I have a startle,” or “I see something in the road that isn’t there” (hypnagogic hallucination). This irrational and dangerous decision-making process has worried me ever since we obtained the data. Waiting to fall asleep before driving is stopped is contrary to every principle of safety on the road.

Drowsy Driving
Although sleep professionals are currently engaged in a public policy campaign against “drowsy driving,” as far as I can ascertain the meaning of drowsy driving has not been precisely defined. It is clear that there are countless people who would show a relatively low (sleepy) score on the MSLT and still be able to drive several hundred miles without an accident.
In this editorial, I wish to suggest an alternative to such testing that is safer and much more likely to be accepted by truckers and all other drivers as well. I believe that drivers can be taught to step back from the abyss. Rather than falling asleep, the signal to stop driving will be the moment of the onset of drowsiness. Drivers can readily learn to recognize this signal. With the proper training, they will respond immediately and never drive drowsy.

Everyone, not just drivers, must learn that there is one and only one cause of drowsiness. If you feel drowsy at any time of the day or night, you are sleep deprived. As we continue to study the subjective side of the coin, we become more and more certain that the premonitory moment of drowsiness is easily detectable. The challenge is to change a lifelong habit of disregarding this signal, or erroneously attributing it to such things as a heavy meal or monotony.

However, we know that individuals can be made to understand that sleep deprivation and sleep disorders collectively are the number one cause of feeling “tired” or being fatigued. They can learn that the feeling of drowsiness, which we have precisely defined, means that sleep is imminent. Finally, they can learn that in any situation where falling asleep has an unacceptably negative consequence, drowsiness is red alert! Remember that sleepy and drowsy are essentially synonymous. Thus, driving drowsy or driving sleepy is completely unacceptable. Driving tired is acceptable if the warning, “drowsiness is red alert,” is always heeded.

As more and more people experience the benefits of eliminating their tiredness and fatigue by lowering their sleep debt or obtaining effective treatment of their sleep disorder, the problem of driving drowsy will be greatly reduced or even eliminated.

In summary, sleep deprivation can be quantified and the strength of the tendency to fall asleep at a specific time can be objectively measured. Upon this scientific foundation, a safer, more alert, and more energetic populace can be created. The key to success for such a public policy safety initiative will be widespread education utilizing the terminology of more precise and clearly defined states of alertness. We will see enormous advances when…

  • people clearly know when they are wide awake, energetic, and not tired.
  • people clearly know that feeling tired means they have not obtained enough sleep or have a sleep disorder, and have accumulated a sleep debt of sufficient size to undermine their waking life.
  • people clearly know that the occurrence of drowsiness in the daytime means their sleep debt is large, and unless some action is taken immediately, drowsi- ness will soon be followed by sleep; and
  • people clearly understand the potentially horrible consequences of becoming drowsy in hazardous situations and respond immediately when the first moment of drowsiness occurs. Drowsiness is red alert!

William C. Dement, MD, PhD, is professor of psychiatry and behavioral sciences at the Stanford University School of Medicine in Stanford, Calif, as well as director of the Sleep Disorders Center and principal investigator at the Stanford University Center for Human Sleep Research. Often referred to as “the father of sleep,” Dement helped create the nation’s first sleep disorders center and played a key role in the establishment of the American Academy of Sleep Medicine (formerly the Association of Sleep Disorders Centers) by, among other things, serving as its first president.

1. Levine B, Zorick F, Roth T. Daytime sleepiness in young adults. Sleep. 1988;11:39-46.
2. Carskadon MA, Dement WC. Daytime sleepiness: quantification of a behavioral state. Neurosci Biobehav Rev. 1987;11:307-317.
3. Dement WC. Daytime sleepiness and sleep attacks. In: Guilleminault C, Dement WC, Passouant P, eds. Narcolepsy. Flushing, NY: Spectrum Publications; 1976:684.
4. Hoddes E, Zarcone V, Smythe H, Phillips R, Dement WC. Quantification of sleepiness: a new approach. Psychophysiology. 1973;10:431-436.
5. Carskadon M, Dement W. Cumulative effects of sleep restriction on daytime sleepiness. Psychophysiology. 1981;18:107-113.
6. Dement WC, Vaughan C. The Promise of Sleep. New York: Random House Inc; 1999.