Imagination is a fundamental capacity of the brain to analyze the surrounding and predict the outcome. For example, if I let go of this apple, it will fall to the ground. It didn’t happen yet, but I imagined it and put it into words. Imagination is nothing less, nothing more. Don’t think that only humans have imagination - animals have plenty, otherwise they wouldn’t be able to come up with new ways of doing things or, say, get better at hunting.

But only humans have the split between conscious and unconscious. Unconscious is basically forgotten imagination - that is, imagined, believed (taken as reality) and then forgotten that it was imagined. The unconscious is deep and vast, and roughly constitutes what in spirituality is called “ego”. All the traumas, all the suffering and all the irrational fears reside there and from time to time bubble up to the surface of consciousness. It is the source of all irrational behavior, burdening emotionality and unsubstantiated beliefs.