I have often wondered about the purpose of sleep. Officially it has to do with rest and re-arrangement of thoughts and memories, for me this is just not quite enough. We see that even flies sleep, do they need to re-arrange there thoughts and memories? Sleep seems to be absolutely vital to the survival of animal, and some other, life forms to the extend that we can almost survive longer without food than without sleep. Since we are at our most vulnerable while we are asleep, you would think that evolution would have developed us in such a way that we would not require sleep, that we should be able to perform the required sleep functions while we are awake and maybe just in a state of rest. What is it about sleep that makes it that important? I am quite sure that there is a big secret hidden behind the purpose of sleep that, once discovered, will open new doors to the understanding of the brain and life in general. I once read about a theory that says sleep is the natural state of all life, to become awake is for life to move into the next phase of awareness. I, myself thinks that sleep has to do with some kind of renewal. We see that even most types of plants goes into a state of sleep during winter. It may not be the same type of sleep that we experience but it may have a similar function. The plant sleep definitely has to do with renewal, old leaves fall off and new once appear in spring. We also know that our cells in our bodies are constantly being replace to the extend that every 7 years we are virtually a new person. Now maybe there are something in the brain that also needs to be replaced and which can only be done while we are in a state of sleep. Whatever it is, it must be aging quite fast so that, optimally, it should be replaced once every 24 hours. I also believe that consciousness can never be switched off unless you die, for that reason we dream while asleep, our brains are fooled into thinking we are awake so that we can remain conscious. I know that officially we go through periods of sleep where we do not dream, I do not believe it, it cannot be proofed and I, myself, cannot remember ever waking up and not know that I was dreaming. We tend to forget dreams very quickly, people who think they do not dream just forget it quicker than others.