A possession of a person is an expression of, a person's personality is taken over by another entity. The person is no longer in control of his own actions.
There is a distinguishing between spiritual and demonic possessions.

Spiritual possession
  • A possession can take hold of a natural thing, animal or human.
  • The possessed can be both benign or malevolent.
  • The possessed person can speak foreign languages, or nonsense.
  • The person can talk in an unnatural voice.
  • The person behaves irrationally and weird.
  • The person has sudden knowledge that is impossible to have.
  • The spiritual possession is believed to be made of either natural and supernatural beings. Eg. by a Muse who brings the art of poetry.

Daemonic possession
  • The possession refers always to a human.
  • In addition to "spiritual possession", there may be physical phenomena. The person can get disfigured, exhibits unusual physical characteristics such as suddenly vomiting blood, metal, needles, glass and more.
  • The person is able to harm themselves or others.
  • The possession always comes from an evil entity.
  • The possession is aways daemonic and non-human (For example an alien or spirit).
Depending on one’s point of view, a possession is made up of 3 to 5 steps.

1.) Manifestation: This is comparable to a chance meeting. The alleged energy finds by chance a person. This can be done by simply having a tantrum, or having a hatred to another person. It can also be done by making a deliberate attempt to contact the occult.

2.) Infestation: Scratching noises, poltergeist activity, problems with electric light and other visible things. Here, the unknown reveals itself. Depending on the strength of "victim", this phase can last from a few days to years. Apparently, this phase is used to break the victim's will.

3.) Possession: Here the victim’s body is taken over by the unknown. Victims report they see their actions as in a movie. The possession can be so violent that the victim falls ill, or even die.

Leading anthropologists (J. Goodwin and S. Hill) have conducted in-depth studies of several cases of possessions. These could be attributed to epilepsy, non-diagnosed diseases or extreme stress. The movie The Exorcist is based on a real event, but the facts are diluted in history as so many exaggerations. Therefore, such a case can always be interpreted.

Thus, it must of course be said that there may be real cases due to paranormal phenomena. BUT:
One should not fear being exposed to the paranormal, just by having a bad day, being angry with  the neighbor, or playing "The Spirit In the Glass". The feeling sometimes of losing control over one's  life is a completely natural thing. A person can under extreme stress, react irrationally and change personality. A sudden change may also be due to brain trauma, blood clots, mental illnesses and many other things. In addition, different drugs (especially anti-depressants) can give you a sense of being a spectator to your own life.

A possession, according to different religions and spiritual circles, can be removed with an exorcism.