Let knowledgeable people correct, but as far as I know, in our brain as a result of its activity, a variety of substances are produced. Among other things, our brain secretes melatonin.
The peculiarity of melatonin is that it accumulates in the body during the day and during the night, from midnight to 5 am, we can observe its maximum concentration. It is the increased level of melatonin that is associated with falling asleep.
Melatonin is associated with the regulation of other processes in the body and the violation of its production is associated with many cancers and accelerated aging. Therefore, try to sleep at night whenever possible (:
If you do not look at the issue from the absurd point of view of creationists, Homo sapiens is the result of a long evolutionary process, ranging from anaerobic bacteria (they do not need air to exist), and ending with the current generation - Homo Sapiens.
Accordingly, the need for sleep gradually began to manifest itself in animals with a developed central nervous system, and in order to fall asleep, they did not need to understand the need for this.
You are not asking a question. , how did people understand that they need to breathe?)