Dreams Are not You. Satan walks on earth.

As an animal, man in nature, should not go into the deep sleeping phases in the way that civilised man experiences. That contradicts with him being on guard against vulnerabilities that he has in the nature in terms of constant threats and miseries surrounding him.
As brain and body of animals evolved more their nervous system became tasked to more house-keeping and information gathering business and his duties of search and finding food, survival and reproduction became more complicated. That made him exhausted in need of rest. While in rest and fall of any movement, vital forces inside him try to shut the entire system into recuperation phase. His eyes become closed to prevent him continuing gathering information and adding to the load of his exhausted body; other senses and means of external communication follow. Only the most necessary activities and those activities that in course of evolution have become adopted with rest state continue to function.
But this period of relaxation does not and cannot continue. Fear and alertness for survival return the body into the awake state. Eyes fall for seconds, ears for a second, nose for less than a second. Then noises, heat and cold and wind and rain interrupt him; most important is the call of duty.
He needs to be careful of his environment. He is vigilant. He is experiencing fear. He is alone sitting in a corner watching the dance floor. A tiny little bad hole starts to converse with him. Bad hole starts to take a picture of his "mind" to use and to aggrandise and to use later. Bad hole takes random pictures. Your eyelids only fall for couple of seconds and fear opens them.
Bad hole injects a couple of random pictures into your mind; you remember them as your dream. Fear, bad holes and dreams become interwoven together. A new creature similar to mind of man but invisible and without body and adversary to man begins to emerge next to man. It digs to open more room for itself and less room for you. Serpent sneaks into the Garden of Eden.
At any occasion the bad hole takes the opportunity to approach to you and carve out a piece of you. Best time is when you are not fully on guard: just at the moment that your body becomes numb and your eyes fall, capitulated and completely exhausted, and the moment that your body returns to alertness, and you are not sure what information just at that moment is the most important to be fetched from your memory, or needs to be acquired from the environment.
Interval between these two in civilised human has reached to as long as ninety minutes, in most natural and safe situations.
How far how deep the bad hole can penetrate and occupy the man, occupy you?
Similar to other natural phenomena it occurs in a spectrum from very weak to very powerful. In weak occurrences most-of-you is you yourself integrated and under your own control. Bad holes are in check and long way to grow. This is among most of population.
If bad holes grow man starts to fight with them. That can consume part of his energy and functionality.
Cases happen that man is completely goes under the control of bad holes. He exists but cannot overcome the bad hole commands, communication and control. He is overwhelmed by constant intervention of bad holes.
What if nothing remains of man and man completely becomes occupied with the bad hole? Then the bad hole has a body of its own. This is rare in nature. Even a small residue of man inside his body fights back with all his might against full occupation of bad hole. (Remember protons are stable but even among them you might find few that disintegrate to other entities - a very rare occasion.)
However, similar to all phenomena, one might observe in few rare occasions, through the history, such a situation that a man is empty of man and filled only with bad hole.
Bad hole occupies an apparently human entity fully with no human residue in its body. What is this, embodiment of bad hole, then? This THING that I said should be shown like chemical radicals inside brackets as [IT]. This THING that is not he or she or even usual it? What is that THING?
Bad holes suffer their host with fear, shame, dis-functionality, and other malaises. Bad hole, as already I explained, reads the mind of its host and brings a picture of the past bad experience synchronised with the present situation to make that bad experience more persistent. What such embodiment of bad hole might look for? There has remained no host for it to suffer what will be behaviour of such a muonium element?

Humans have experienced occasional occurrence of such entity. They have called it Satan. An embodiment of human shape that is full of evil; the perfect bad hole. There is no hooves, horn and tail and no fiery eyes and no fork teeth.

Satan looks for, searches for someone to suffer in place of the host that it lacks. Satan looks to find the Perfect Human among the human aggregate.