The basics of any laboratory report or essay exam question ever encountered begins with defining the given terms - what is sleep and what is not sleep? Sleep is known to account for one third of one’s lifetime; Thomas Edison claimed it was a waste of time (which is probably why he spent so little time doing it). To start with, Edison is wrong, and sleep is more than just a bulk of life spent on lying down “out cold.”

Harvard Medical School’s Health Sleep Lab defines sleep as a “state that is characterized by changes in brain wave activity, breathing, heart rate, body temperature, and other physiological functions.” A breakdown of this rather vague attempt describes sleep as a period of reduced activity and decreased responsiveness to external stimuli.

Some would like to think that sleeping is equivalent to nothing happening at all; for example, when asked by a roommate on what one has been doing, one might just as well shrug his shoulders and respond, “Oh, nothing. I just took a nap.” Although not much can be seen from the outsiders (that is, from the viewpoint of the spectators and not the sleeper himself), in fact, so much is going on in the human body.

After shutting one’s eyelids, one falls into a recurring cycle of about 100 minutes which is divided into rapid eye movement (REM) sleep and non-REM sleep.

Non-REM sleep consists of three stages: light sleep, true sleep, and deep sleep. Light sleep involves the loosening of muscle activity; true sleep takes the person deeper, slowing down the breathing pattern and heart rate, and takes the biggest bulk of what humans define as sleep.; deep sleep, as the name suggests, entails lowest levels of breathing and heart rate, limited muscle activity, and delta wave production in the brain.

REM sleep takes place during the earlier part of one’s adventure to dream-land – about 80 minutes into sleep. What sets apart the REM sleep from the non-REM sleep is that the brain is very active during REM periods, in spite of the person’s being unconscious. Moreover, breathing rate and blood pressure actually rise during REM sleep unlike non-REM sleep. Another noteworthy characteristic of REM sleep is that it is when people dream and that the body is effectively paralyzed during this time.

Okay, so such and such happen while we sleep, but is there a compelling reason to sleep other than the fact that one feels sleepy? What if one did not feel sleepy at all? Would that person be self-sustainable without sleep?

Well, sleep scientists say otherwise - it is true that sleep is a period of reduced activity in general, but without this period, one would not be able to continue with even the simplest of all daily tasks, be it physical or mental. For one thing, our bodies “regulate sleep in much the same way that they regulate eating, drinking, and breathing,” according to Harvard Medical School’s Health Sleep Lab. And since few would deny the critical role of eating, drinking, and breathing, it is natural to follow that sleep serves a similar role.

For instance, one can think of sleepiness and sleep as analogous to hunger and eating. A good night’s sleep makes us feel better, happier, and more energetic, and probably allows us to perform better on quizzes and social interactions, just as having a good meal would benefit us in a strikingly similar way.

While a more scientific answer to the reason for sleep remains a group of plausible candidate theories, they are more or less centered on the same motive: a powerful internal drive that pushes us to sleep so that the body conserves some energy, recuperates itself, restores damage, forms new neural connections in the state of inactivity.