Complexity and related phenomena exist as at least as “objective” and primary aspects/elements of the world as matter, space, and time. On the other hand, space, time, and matter become more and more subjective in modern physics. Complexity causes “something new” to emerge at the level of the whole complex system, which is not present at the level of the elements of this system and cannot be fully reduced to the interactions between these elements. This fact concerns both simple systems, such as atoms composed of a nucleus and electrons or (macro)molecules composed of atoms, as well as very complex systems such as living individuals built of (macro)molecules, organelles, cells, and organs, and conscious brains composed of networks of neurons. In other words, the dynamic complexity consisting of a special concrete spatiotemporal organisation of matter/ energy is as real as space, time, and matter themselves. Therefore, one can speak about the “objective” existence of such a “subjective” phenomenon as (self-)consciousness. The last phenomenon constitutes an aspect, epiphenomenon, or “by-product” of the functional complexity of the (part of the) neural network in the human brain. Self-)consciousness is equivalent to a certain kind of such complexity and must emerge as a necessary aspect of an appropriately organised dynamic neural network. Therefore, for instance, zombies cannot exist or are even nonsensical. Each dynamic state of the neural network underling self-consciousness is univocally related to one psychic state, and inversely. It is postulated that the mind-body problem can be explained/resolved by a special kind of complexity, which consists of recurrent self-reference, directing on itself the “cognitive centre” in the neural network in the human brain.