I also 'saw' ghosts or figures when I was little and naive. Then I grew up, found logical thinking and they all suddenly vanished! No more sightings.

You see what you want to believe (either you'd like it or not)

Did you physically see a ghost/figure leaving or entering the 'possessed' man? If you did, do you have physical evidence of it?

Almost all cases of 'possession' are basically people with schizophrenia, drug abuse, stress, or some other factors that affects the brain. That's why mass hysteria usually happens during times of stress and tension (examinations, tests etc.).
No I don't have proof. In this case, there's more need to prove that ghosts DO exist than not. Because while current scientific understanding doesn't outright disprove ghosts, the existence of them is extremely unlikely. It's just illogical.

So it's not that I have to prove they don't exist, but you believers that needs to prove that they don't.

Also, I don't, that's why the need to go to the professionals to get evaluated.

P.S. Oh and I did see 'ghosts/figures' when I was little (age < 13), but I learnt it's all basically bullshit and it's just your eyes and brain trying to fuck with you.

sigh...

Where did you get your science education? Intangibility or the fact that something is quantifiable or not isn't a problem.

That's the thing! I couldn't say because I don't know what kind of condition you fucking have! There are a lot of factors, a lot of variables. It's not all black and white, 1s and 0s! For all I know you might have a mental condition that makes you hallucinates and see things that isn't there.

lol wow there's no such thing as too much science. Kau ingat makanan ke apa.

No, science can't definitively prove god or heaven or hell, but no one can provide concrete evidence for them either.