Demons psychologically represent ideas in the mind through which you torment, persecute or harass yourself. They may reflect some idea that drives you to disobey God's instructions. [alcohol and sex are often such ideas] Thus fighting off demons would imply defending yourself against some idea of this nature.
Being possessed would imply being under the control of an idea that is not in obedience to God; that it has gained mastery over you. Looking in a mirror implies taking a look at your self image. When possessed like this, your self image does not present a pretty picture. The face, with one eye closed and one slanted, suggests a self identity that is not a reflection of the real you.