I once thought as you did once to be honest. However, experience has proven me very wrong as I work in the mental health field. It is a common error for people to not understand the difference between mental health and spiritual issues and sweep everyone under the same roof. For me I have a very strong background in Biology and Psychology and in my earlier years totally ignored the idea the demonic even existed. To be fair I approached life more like a atheistic scientific skeptic.
That changed as I met people who did not quite fit the standard molds. To be fair modern science has a long way to go in understanding of what causes mental problems. We offer pills and various therapies but often are clueless to the causes of the disorders. I feel that there are many biologically and psychologically causes disorders but I have also encountered some strange phenomena.
It is not usually like many of the movies which do no justice to what a possession really is. It can be voices, feelings, things you see (very easy to confuse with schizophrenia) but usually it is thoughts. The end result is similar in that it distorts the person away from the image of God. The result is a person who is more in line with how that particular demon or demons think and act and are thus able to create a “possession”. These are not usually perpetual states but periods where the person is taken over and then they return to normal. They may or may not have memory of the event.
It is very good at hiding and will often try to masquerade as a mental disorder. I found I was dealing with what I originally referred to as something that appeared to be a “sentient disorder” while working with various people. I could easily have done what most other professionals do and continue to recommend a treatment (basically a bunch of pills and maybe a decent counselor) but I decided to dig deeper.
What I discovered was what I called “religious allergies.” Aversion or hostility to holy objects (even hidden ones). Things that I got as wedding presents (like an Icon from a monk) or a old bottle of excised salt collecting dust on my back self. These allergies would occur during the times I was dealing with the “sentient” thought process of the afflicted person. Considering that traditional treatment was not working and talk therapy was revealing a very odd disorder that appeared to be sentient and religiously intolerant I decided to step out of the mold of medical professionals and seek help.
I looked at Medical texts and Psychology journals which generally scoff in a very prideful manner that this stuff does not exists and its just made up. Some protestant friends offered to pray and baptize one person who agreed and then they started getting crippling nausea and headaches. I took them to a friends Jewish temple and the same thing happened on the way there, not during the quorum, but flared up immediately after leaving the temple. Puzzled I started to do more analysis of the person to make sure this was not a grab for attention, or just some other weird ploy or disorder.
A priest I knew growing up recommended putting excised salt in food they like. When offered the food they rejected it even though they asked for that very food. Next he recommended some deliverance prayers for them (they were raised New Age) sure enough some of their symptoms disappeared after praying them. What followed next is a year long saga of me trying to prove to myself this is not real as one thing after another that I dealt with was explained by exorcists (moving headaches and stomach pains, religious aversions, throwing up during rosaries, etc) but science offered some bland explanation like somatoform or multipersonality disorders but no real effective treatment options or causes for these people.
There is MUCH more that I experienced and had to deal with but I gave you a snippet of my life experience to open your eyes. The devil is real and likes to stay hidden. My life is much harder now that I acknowledge this exists thanks to people I have to deal with who think just like I did and you do now. The field of mental health tries to teach us in basic psych courses that demons were once thought to cause mental disorders but “we know better now”. God ultimately proved me wrong and it was a very difficult transition. Now I can be openly mocked and discredited by multitudes of atheists and lukewarm believers in the field.
However, I am here to help heal people even if it means being assaulted for the rest of my life. Science does NOT have many answers in the mental health field. Many doctors confide to me how they feel they are “wasting their talent” in Psychiatry since it is so difficult to treat even basic depression. I have met many people healed though Christ. Psychology can open your eyes to what issues you have, Biology can heal many problems of the body, but Christ is very effective at healing issues of the mind (demonic or not).
I apologize for the long post. You have the freedom to utterly disregard my story but humbly I caution you that you may find out the hard way like I did. Being unprepared for the onslaught of spiritual warfare was not fun or easy. Not every thought that prances into your head is your own.