If your dream that you are having focuses on the idea of demon possession then this has a slightly different twist on the definition of the dream. If you have a dream in which you are possessed by a demon and it starts to use your body as its own while you have no ability to stop then this basically means that one of your personal demons is monopolizing your time in real life. You are being totally consumed by thoughts about one particular troubling memory, one sad thing that you keep being forced to revisit even though it causes you so much pain, etc. You can't let your thoughts and your individuality be sapped out of you y old memories that you can't stop. Do the best you can to escape from this harmful thought process.