In humans, the autonomic nervous system is a control system that acts largely unconsciously (just how largely is a subject of some debate, but almost entirely is fair to say) and regulates various bodily functions such as the heart rate, digestion, respiratory rate, pupillary response, urination, and sexual arousal. Our immune system, though not officially a part of the autonomic nervous system, is also intimately associated with it, and mistaken or inappropriate interactions between the two systems are thought to play a role in the development of many chronic diseases involving both. Although this has also been challenged by some, the immune system is also generally agreed to be entirely out of our conscious control. If we do have some conscious control over the immune system it is most likely only at the edges, and at a holistic rather than fine detailed level. Both systems are scarily complex and textbooks and research papers abound in both fields. There are undergraduate college courses and graduate programs dedicated to each, and many a Ph.D. and MD have made entire careers out of studying them. For purposes of this discussion all you need to know is that it is widely believed/understood that human life would be impossible without either or both of them.
I argue, and I am sure others have as well, that there may be an absolute requirement in embodied conscious/intelligent beings for such a system or systems. No doubt they could take many different forms however, on some level, a conscious, embodied being must have some aspects of its bodily function that are out of their direct conscious control. After all, how could it be possible for a being to exist that had to have complete and conscious control over every aspect of its bodily functions at all times? The amount of focus and energy such an undertaking would require would seem to leave no time to dedicate to any other activities that are typically required of a body such as taking in energy in some form, removing waste, etc. I also happen to believe, though this is not a widely shared opinion, that a physical body of some form is a hard requirement for consciousness and intelligence. This opinion is highly unfashionable in the age of A’I” and machine “learning” where bodies are no more than an afterthought. Today, talk of bodies is largely dismissed as “anthrocentric” thinking or “behind the times.” Consider me behind the times because I happen to be a proponent of this position for a variety of reasons that are much to complex for this space, and not relevant to the matter at hand. If you do accept this then my case becomes much stronger, if you do not then it becomes almost moot. No matter your position on the importance of embodiment to consciousness/intelligence thinking about the question I have posed is a very interesting and leads to many interesting and strange places. For the aspiring science fiction writer the concept seems delicious with possibilities. As I have no such inclinations I offer the idea free for appropriation. It has probably already been used before anyway. Almost everything has it seems. Originality for the science fiction writer is the most difficult of topics. Well that was a strange place to end up. lol!