The physical side of what occurs when we sleep is comparatively easy to understand. Although the specifics of what occurs at a molecular level is not fully known, the general physiological circumstances are understood. Our bodies slow down or suspend their aware-state responsive activities and then boost their maintenance and repair functions. Absorption of needed resources from the digestive tract is increased, tensions from active life are relaxed, the sifting of detrimental molecules by the kidney and liver is heightened and the immune system operates at a higher efficiency to deal with health problems, whether from an internal or external cause. Essentially our homeostasis, the body's balance, is restored from the disruptions that naturally occur during the active portions of our day.
While awake we undergo perceived stressors, consciously or sub-consciously. Such stressors induce our bodies to produce corticosteroids to maintain them in a state of preparedness to face whatever challenges may occur. Acute stressors, such as a fright, stimulate hormones such as epinethrine, more commonly known as adrenaline, to surge dramatically. This is a natural reaction to prepare us to either flee or fight the cause of the stress. In modern society, neither response tends to actually be appropriate in many situations, but the body still automatically responds in this way. Even when the stresses of our life are not this up front, we still produce considerable amounts of these hormones, keeping us in a state of preparedness.
When we fall asleep, the production of these hormones reduces significantly. We are now relaxed and our body recognizes that we no longer need to be prepared to run away or fight some indeterminate threat. Besides preparing us for such, corticosteroids also have a suppressive effect on two of our bodily systems; the digestive and immune systems. Therefore, once we are asleep and the amount of these hormones in our blood has reduced, our digestive and immune systems actually increase their activity by a considerable amount.
This is also why, when there is a need for either of these functions to increase their activity, we find ourselves feeling tired. If we have just eaten a large meal we feel the desire for a nap. This is probably even better displayed in large carnivores. Nature films often show large predators such as lions or wolves sleeping around the remains of a prey animal they have gorged upon. They have expended considerable energy bringing down the prey animal. After feeding, their bodies induce them to sleep so that they will digest the maximum possible from what they have consumed, so as to replace the expended energy. The digestive system runs at its most efficient and active state when the animal is sleeping.
The same applies to the immune system. Corticosteroids have been demonstrated to suppress immune system responses. This is a perfectly natural and logical survival response to stressors. Diseases may eventually threaten an organism's survival, but environmental stressors, such as the proximity of a dangerous predator, are far more immediate. The body recognizes that there is no point in eventually succeeding in overcoming a disease if you have been killed by a predator in the meantime. When it does not need to concern itself with such outside threats and is therefore not producing significant amounts of stress hormones, it can devote itself to defensive measures against internal threats.
The immune system goes into overdrive and attacks any infections by bacteria or viruses, or dangers such as cancers caused by somatic cell mutations, that threaten the continuance of the individual, whether human or animal.
What happens on the mental side is still largely a mystery. We sleep and we dream, but what is dreaming? Theories abound and scientists measure brain-wave activity, but why we sleep is still an unknown. The physical requirements mentioned above could be catered for by rest, without the unconsciousness we experience in sleep. And we are not alone in this, all higher lifeforms sleep, whether lower lifeforms such as insects do as well is uncertain.
Studies in sleep deprivation have shown that long periods without dreaming cause mental psychoses to develop in those so deprived. So what is it about dreaming that is essential to the well being of all of us? Some believe that in dreaming we rehash our "real" experiences so as to assimilate them into our world picture. Others consider dreaming to be our interpretation of the random firing of neurons in the brain and therefore of no particular consequence. Yet others consider dreaming to be showing us realities we would not otherwise perceive, visions of past, present or future events we should not be able to know or experience.
Up until now, this article has covered factual reality and fairly standard conjecture, now it is time to delve into the realms of possibility and imagination. Surprisingly we will do so by considering the latest theories in physics. Work on a Unified Theory to combine quantum physics and relativity has indicated the feasibility of multiple dimensions and possibly a multi-verse in which our visible universe is but one of many.
Could it therefore be that when we sleep our mind slips the chains that bind it to our brain and roams alternate worlds? Might it not fix on those who are our alternates or equivalents in those worlds, sharing their memories and experiencing their lives during that time? Might dreams change direction or context so rapidly sometimes, simply because we have moved on from one alternate's life to that of another? Do our memories of our dreams rapidly disappear because when our minds re-seat themselves in our brains they reattach to the memories stored there chemically, losing those of the brains they were attached to during their travels in our "sleep"?
The possibilities seem endless and the current reality is that we really do not know. Measurements of brain activity are exactly that. We do not yet have any idea of what creates our minds, our awareness. Although it is almost certain that our minds are propagated by our brains, are they also limited by them? Has the concept of soul been created unnecessarily? Might it not be that minds and souls are basically the same thing? How fascinating to think how much wider reality might be and how much more of it we may be experiencing than we realize!