TV is entertainment ! I would suggest that in every case on television you are watching an actor plying his or her trade. Certainly a trance medium may demonstrate voice changes or an altered physical state whilst working, however this is should definitely not be classed as possession.
The history of spirit possession and the rites of exorcism reveal valuable clues into the nature of the phenomenon. Although spirit possession is commonly considered to be an objective threat to humankind, it remains an exclusively subjective experience. The experience itself is dependent upon the beliefs, norms, customs, and expectations of society.
In Haitian voodoo the possessing spirit enters the head of the victim and displaces the person's soul. In the West malevolent spirits generally attach to the victim's aura causing various disturbances; inspirational spirits, on the other hand, typically cause soul withdrawal resulting in total possession. The Zar spirit mainly possesses women who are experiencing domestic tension; it appears to leave after the women's needs have been satisfied. Spirit possession ebbs and flows depending upon the current belief system operating within any given society. Possessing spirits have repeatedly sought to possess particular subgroups within a population. Japanese history indicates that the wives and daughters of Emperors are particularly prone to possession. Within societies where spirit possession is validated, it functions as a last resort for oppressed citizens to acquire attention and get their needs met.
Belief in spirit possession is the prerequisite for the existence of entities which interfere with the living. It is simple: if a person does not believe in spirit possession he/she will not experience being possessed by outside beings, whether the spirits are evil or inspirational. Where belief in possession is strong, entities are busy possessing individuals and causing all sorts havoc upon the particular society.
Multiple personality disorder (MPD) and schizophrenia are sometimes associated with spirit possession. In MPD the victim assumes a solidified identity of two or more "persons". The personalities can be incredibly diverse claiming to be of a different gender, race, age, and family origin. IQ levels have been known to change between the different personalities; distinct personality profiles accompany each identity; and personality specific mental disorders may also occur. While it may be tempting to associate multiple personalities as being discarnate spirits, the history-specific nature of each personality arising from the victim's own past makes the spirit possession hypothesis improbable.
Spirit possession serves several functions in our society. For those who firmly believe that they are possessed, an exorcism may be the only means by which to evoke a cure. It is often turned to as a last resort for those experiencing obstinate psychological disorders. More commonly it serves as a form of psychological disassociation. Thus deep, troublesome psychological material need not be owned by the individual if he/she adopts the ideology of spirit possession.