Getting enough sleep is widely recognized as a necessity for enjoying good and robust health. Why is this so?

It is no different than the physical demands on the body from exertion of any kind, whether physical labor or a sporting activity, there are limits to what the body can do when called upon again and again and again to perform. There must always at some point be a period of rest and quiescence to have a chance to reset things, to rebuild inner stores for energetic utilization, and the clearance of by-products of metabolism which can become toxic if they build up to too high concentrations within the cells. It takes time for the circulation to clear these things away as well as to bring replenishment with nutrients as well as oxygenation of the cells, and so on. When the body is overextended in physical activity there needs to be a period of recuperation, otherwise things will start to break down when pushed outside the limits of tolerance. The same is true on the organ and tissue levels, there must be some break in high-level activity to allow the tissues to catch up and take care of these housekeeping needs. If that is not done, there will begin to be symptoms of all kinds signaling distress, feelings of discomfort, becoming less efficient, and with neurologic impairments that will start slowly and to a small degree but then build in intensity and the severity of the consequences for cognition. So physical endurance is mirrored in mental endurance as well as cellular endurance—all have limits and need to have periods of rest.