The ghost of someone still alive.

I'm watching this docuseries that is taking a look at ghosts and hauntings and alternate theories on what they are. It says that it is possible to have a ghost haunting a house from someone who is actually still alive.

So....It says that if a man/woman is possessed by another spirit, then the original man/womans spirit is pushed out of the persons body and becomes a ghost that could haunt the place he/she died. Errrr...was pushed out of their body.

Then they would haunt that location while their body, now possessed by another ghost, would continue life as that same person. Only, it isn't that same person...and voila! A haunting from someone who isn't dead.

It's pretty confusing but does anyone think something like this could actually be true?