Call it real or fake, it's there but there are no concrete evidences if that's a possession or a malfunction of the mind. What I mean by malfunction is a sudden trigger of a certain part of the mind or a syndrome. There are many reports of possession in my area and priests from far towns help to solve the problem, they say it's a clear case of possession. Anything can be able to possess but only in certain conditions like a weak soul and more... :3
First of all, yes, possession is a real thing. But this need clarification.
There are several "kinds" of possession, for example, if you ever try a ouija board(I hope neither of you do), keep in mind that one of your friends is moving the glass, because he has been possessed.
In order for the glass to move, a random spirit possess someone, it tends to be the weakest soul.
This would explain why we all heard stories about people having horrible experiences using a ouija board, but it doesn't always end in a frightening, cruel, strong possession, sometimes the spirit lets the people alone when things are finished.
As to the demonic possession we all know about, well. They exist, but they are not very usual. And as you would expect, people who are possessed will keep it as a big secret.
I've seen cases of people being possessed, and the things which happened to them were not normal at all, nor could be explained as a "mind malfunction". For example, their eyes randomly changed their colours.
I remember when I was little, I used to be a Jeh***hs witness. Well this man had spray painted some stuff on the kingdom hall and the next night during the meeting we could hear him screaming like hell. The next day there was a news report that a man had been killed, no footprints, fingerprints or dna, just a dead man who is now missing his pupils indicating he saw something extremely bright. Not exactly a possession but it may give you some insight into the spiritual. Everyone still believes a pissed off angel killed him