I agree with the possession phenomenon. It is beyond traditional psychology. But there is a corresponding physiological part too - chemical imbalances.
I think we underestimate the power of the mind while forgetting, or simply not being aware of, its place within the human hierarchy.
As a high school student back in the late 70s I watched hypnotists perform some rather amazing tricks on kids in my class who foolishly volunteered and went up on stage.
Pretty funny stuff, but my takeaway years later is the power the mind has over the emotional and physical aspects of the body. If the mind believed, the body responded accordingly.
I know that the mind's not the top of the chakra totem pole, of course, but it is above the physical and the emotional, as the hypnotists repeatedly demonstrated.
From a spiritual perspective, human rationalism is often cited as one main cause of our/humanity's fall and that rationalism is easy for Satan to manipulate at will in an uneducated, unanchored or damaged soul or a soul with an undisciplined free will.
The Trickster's two trick garden pony is to convince us that:
a) he, Satan, the Trickster himself, doesn't exist and
b) your reality is "whatever you want it to be, man."
With a little time and worldly, situational motivation, fundamental transformation of an unanchored soul is especially easy in these days.
Unfortunately, our Modern Psychology likes to ride Satan's garden pony while pretending its a rodeo cowboy.
Giddy up, Cait.