Obsessed Obsession
We are all obsessed or possessed in various ways. For instance, we may not be able to walk down the street without shoes, or be unable to appear in public without a collar and tie, or properly shaved, or with the wrong people, we are thus literally possessed by social codes, fear of looking a fool, and so on. Being possessed by such things our actions are controlled by such fears. These are the demons that rule our life and enslave us, and that were spoken of in the past as being cast out. These factors are often symbolised in dreams as an obsessing agent. Autonomous Complex
The agent need not be your own fear or drive however. There are other driving forces, such as social pressure, the and great external forces such as government or corporations, that act upon your psyche.
Being possessed by such things means our actions are to some extent controlled by them. The unconscious pictorialises this situation by using the images of demons or dark shapes. These are demons that rule our life and enslave us. It is such demons that Jesus cast out in the Bible stories.
In past cultures the ideas or fears which obsess us would have been described as an evil spirit or ghost taking over the person. This is because the irrational obsession takes hold of us against our will, so is quite an accurate image.