Each of us has a specific daily sleep requirement. The average sleep requirement for college students is well over eight hours, and the majority of students would fall within the range of this value plus or minus one hour. If this amount is not obtained, a sleep debt is created.
All lost sleep accumulates progressively as a larger and larger sleep indebtedness. Furthermore, your sleep debt does not go away or spontaneously decrease. The only way to reduce your individual sleep debt is by obtaining extra sleep over and above your daily requirement.
The powerful brain mechanism that regulates the daily amount of sleep is called the sleep homeostat. By increasing the tendency to fall asleep progressively in direct proportion to the increasing size of the sleep debt, this homeostatic process ensures that most people will get the amount of sleep they need, or close to it.
The elevated sleep tendency together with the associated drowsiness and an intense desire for sleep would ordinarily prevent most people from becoming dangerously sleep-deprived because they would go to bed early, or sleep late, when such excessive daytime sleepiness occurred.
However, in our society we are prone to ignore or resist nature's signal that we need more sleep, and we often resist far too long. At this point, we cannot resist falling asleep. Depending on when and where this happens, falling asleep can be tragic, or merely inconvenient. As far as is currently known, nothing can change an individual's fundamental daily sleep requirement.
(Source: William Dement, M.D., Ph.D, Stanford University Center of Excellence for the Diagnosis and Treatment of Sleep Disorders)