I believe that the term ghost refers to only human energy. I also believe that they can exist on different levels. Like when you are born into the physical plane you grow and evolve physically and mentally. I believe that when our physical body ceases to be alive that the spirit energy enters into an existence kind of parallel to ours and this is at the lowest or youngest in spirit existence and most photographs that we get are of spirits at this level. Then you grow and mature also as a spirit going from this lowest level upward but they are always able to return downward to the parallel world to ours but most have no desire to return until they are born again. Full body apparitions may be an example of a more mature spirit.

             Now as far as being hurt or possessed I think that whenever spirits try to make themselves known to us sometimes in doing this they may just intend to touch or speak and somehow end up coming through too strong thus causing a push, physical pain, or some mental trauma to us. Kind of like shouting at someone and they don't hear you and they keep shouting and shouting louder or touching and touching harder until finally it comes through much stronger than intended. So for someone who is not capable of perceiving and receiving their attempts to communicate, it is they who usually end up with the over emphasized physical or mental manifestation.  I believe that this resulted manifestation is then interpreted as a possession or attack.

              Now there can exist other intelligent energies besides ghosts. Most people use the word ghosts and spirits to mean the same thing but they actually do have different definitions. Spirits aren't necessarily human. I tend to use both when talking about human ghosts and prefer to use the word spirits. This is just what I believe.