I know 90% of the science behind possession. I will keep improving this answer based on my experiences. Here it is- (since it has happened with me starting 4 years ago at the age of 43 suddenly out of the blue and all I have done is observe scrupulously my destruction). Also just FYI I am a telecommunications software engineer and a research scientist in nanotechnology. I am very scientific and rational in nature but also very spiritual and don’t think there is a conflict between spirituality or science. It’s about finding the truth. Now the process of possession as experienced by me- (I’ll write it as a phenomenon)
Evil spirits or demons connect with you (I don’t know how they do this, but in my case they came from family members). Once they connect with you they start bombarding you with all kinds of sensory media- voices, smells, images and tactile sensations to keep you occupied and lose your strength of self. When this happens you are not able to be yourself anymore. You are constantly listening to the voices, making sense of it, tolerating the tactile sensations on the body, seeing images, etc and are basically you are occupied with the torture. Mind cannot be independent or in the present. Sexual contact and communication are their two main modes of attack. Since they or the stuff they insert (yes they do this) can be “felt” they can do movements in you to cause sex (rape) which they start and continue forever. They also do back and forth movements through you continuously that starts harming the body physically. Over a year or two your body begins to break down and become weak. You can feel pain everywhere and you are nervously exhausted because their tortures are continuous. Eventually they harm your neurological circuitry so badly that they can insert more and more “stuff” (don’t know what this is too but it is organic, maybe a part of them) and keep on doing movements- painful or sexual. Along with this they keep the voices channel active as well by talking continuously. I think these movements give them some energetic advantage- something is transmitted from our bodies continuously to them while these movements happen. May be it is sexual energy or just plain neurological energy. They feed on that, harm day and night and live. This is their way of life. They have told me that- this is the only way they can live. They also tell me this way they don’t have to do any work, they can escape all responsibility. Also as they keep breaking down the body, their entering or inserting stuff inside us becomes easier. I can feel that my boundaries have become very open unwillingly. I feel extremely violated.
Now since they are “very methodical” in their approach to destruction I am willing to believe it is also possible that instead of some demonic spirits they are actually demonic humans who have cracked this code of breaking human barriers by doing harmful cultish activity and know how to live attached to you like parasites. I think it is possible since in meditative communities it is quite customary for folks to be able to hear others thoughts or get access to others sensations- there are righteous ways to do it and there are cheap tricks especially for those with no moral limitations. But it is true that it is either evil spirits or demonic humans doing this. If it is demonic humans I mean deranged psychopaths who may have already killed dozens of people and are on the path of depravity. These are demonic entities for sure.
Possession is real because in 4 years from hearing voices for the first time at the age of 43 and being a highly functional and happy adult I have become bedridden, jobless and suicidal. I can’t tolerate the physical harms anymore. None of this is a delusion.
These are also the experiences of many schizophrenics which I have read about in scientific papers but sadly psychiatry is not able to wake up to this reality. They have lost faith in Christianity so much that any talk about demons or demonic forms makes them run away from it. I don’t care what these things are but they harm brutally and can get away with it without anyone believing it leaving this to be a very silent illness. My torture is a secret, imagine my plight. I was an engineer doing nanotechnology research once very happy in life.
Our society needs to wake up. I have practised Vipassana meditation for 15+ years , it being Buddhist in origin- in all meditation centers all practice always starts with the first prayer for protection against demonic entities especially warning them to not harm humans especially those who are meditating. You can check Atanatiya Sutta and it’s translation. Also the greatest Buddhist monk of all times Ledi Sayadaw who is responsible for the rise of Buddhist teachings on earth in the past century has written a book on how demons cause disease and how a wakeful society can prevent this from happening. People of high meditative attainments can see evil spirits. I don’t know why this is so hard to believe especially when there is enormous suffering for the patient and all world cultures accept it. Schizophrenics need to be saved! Please be open to different possible realities. The harm is too much! And crimes against humanity are happening.
You can checkout my other answer here-
In the clutches of Mara 