Obsession, in occult philosophy, is a state in which the human mind and spirit are thought to be besieged by the devil or some malevolent demon causing the person to exhibit strange actions that are inconsistent with his usual behavior. An individual may also have an obsession with a supernatural entity, such as a ghost, which occasionally compels the person to display bizarre behavior.
In spiritualism obsession is believed to be caused by a discarnate spirit or spirits trying to take complete possession of the living for the purpose of selfish gratification. Trance mediums utilize such a situation to develop a cooperative relationship, while the medium’s normal self is in temporary abeyance during this period of control. Some mediums specializing in this area are able to help possessed persons; like Christ, they cast out devils–demons and evil spirits. This process is similar to dybunk practiced by the Jews. The first mentioning of an evil soul possessing another person in the Kabbalah was in 1571, and also in a legend about the imminent Kabalist Lauria.
Sometimes exorcism is used to drive out the malevolent entity. Other mystical traditions have their own rituals of getting rid of the unwanted entity.
But, what is an unwanted entity? Some people do not like animals nor have pets while many modern Neo-pagans consider their pets their familiars. Children often have imaginary playmates; adults who go around talking to God, Jesus, the saints, or imaginary people are called crazy, but praying to God, Jesus, or other divinities in a church, synagogue, or mosque is deemed all right. Prayer has approval, whereas, imaginary companionship does not, which leaves the question, is this hoe obsession judged and determined. A.G.H.
Greer, John Michael. The New Encyclopedia of the Occult. St. Paul. MN. Llewellyn Worldwide. 2005. pp. 337-338
Riland, George.The New Steinerbooks Dictionary of Paranormal. New York Warner Books, Inc. 1980 pp. 207-208