I've never seen it.
Every time it has always been mental illness.
Quite scary enough though!

Elementals are real and can be of either a positive or negative nature, the negative ones would be similar to demons.

Then theirs the Qlipoth, evil demons and shells of the very evil who are dead. VERY nasty and the truly, very evil ones of this world will get to join their ranks, such is their reward. All their riches and power won't help them.

I've never seen or heard of one of these beings actually Possessing someone but if one is set upon you, life will be very bad indeed and I suppose that would be close enough, haunted and harrassed yes but not possesed and that would require a banishing not an exorcism.

An exorcism could do psychological harm, reinforcing the patients psychosis and in the other case probably amuze the Qlipoth.

And then of course theirs the ethical dilemna of beating up on Demons, even if they like it...

LOL

Best Wishes,

Frater