I do believe in unseen spirits. In the religious community I belong to there are only three kinds of Spirit beings, the Divine God, His spirit angels, and those who opposed Him, the spirit demons. Not all believe on these categories, but many nevertheless believe that there are the unseen supernatural beings. This video will let anybody who does not believe in the unseen supernatural and paranormal think and reconsider, although these are just opinions. Here is the definition of demon possession from wikipedia.
"...is believed to be the process by which individuals are possessed by malevolent preternaturalbeings, commonly referred to as demons or devils. Obsessions and possessions of the devil are placed in the rank of apparitions of the evil spirit among humans. It is obsession when the demon acts externally against the person whom it besets, and possession when he acts internally, agitates them, excites their ill humor, makes them utter blasphemy, speak tongues they have never learned, discovers to them unknown secrets, and inspires them with the knowledge of the obscurest things in philosophy or theology." -- https://en.wikipedia.org/wiki/Demonic_possession