From my 'shamanic' perspective, I would understand this to be a manifestation of inappropriate energy. This energy found a comfortable home in an energetic hole that was there due to you not being energetically fully powered up. In Shamanic Healing the approach is to persuade the inappropriate energy that it is better off somewhere more appropriate and to bring power back to the person to fill the space so that nothing else finds it an attractive spot!
I personally find it unhelpful to think of anything as 'demonic', just inappropriate. In this way it is much easier to negotiate a shifting of energy with love and light.
wishing you peace and power
Black Wing ~~>~~