Signs of possession

Possession, unnatural movement of objects,language the original person couldn't possibly know, Depression, huge loss or increase in weight. Mood swings,unusual outbursts of violence and cussing. These are some of the signs of possession. So is it possible to be possessed and not even know it? Is it possible to live a normal life while a demon is controlling your every move, your every thought? I personally think it is possible, I mean why not?