Regarding demonic obsession: I've experienced this and so has B. [another friend]. There are interesting parallels
1) You feel like you're going crazy
2) During the initial experience, everything looks red-- as if a veil of blood was over one's eyes.
3) There is a very strong sense that the urges and preoccupations are out of control and foreign
4) The psychological state does not feel entirely human, at the mildest at the furthest extremities of psychopathology
When I got hit, I also felt inexplicably hot. I had to strip naked in order to stay within the most basic comfort zone and then locked myself in my room to protect mom and the cats from my hard-to-resist compulsion to cut them open and rape the wounds as they died.
B. just became violent and her husband at the time said her eyes looked crazed and wrong, presumably the pupils going big. That's actually what caused the divorce. Instead of going to a spiritual person, he had her thrown in a mental ward.
With me, I contacted a few other people who did a remote exorcism. I kept myself busy by fantasizing doing what I described above while stabbing a bookcase with an icepick hundreds of times and masturbating about ten to twenty times. My libido was utterly inhuman too. So, during that period was when I got my insights on how demons thought about stuff. Pretty terrifying.
Demonic obsession begins suddenly. It goes on and off like a lightswitch. B. reports similar. My rational mind was strong enough to realize that something was dreadfully wrong, and was able to restrain myself. But my emotions and preoccupations were totally displaced and usurped by the invading entity. I also knew I was me, but my personality was largely suppressed.
In short, demonic obsession per se is not subtle at all.
But demons tinkering with minds in subtle ways is real, it's just not the same phenomenon. Or perhaps a very very downgrade version. I sort of look at demonic obsession as a wholesale displacement of the emotional structure of the victim which can be expelled with minimal scarring. Demonic tinkering is basically permanent, inner scarring. It takes more work to purge.