My own guess is that some visual, auditory, tactile and smell/taste hallucinations are real spiritual experiences, which upset the balance of the mind in many people and this upset balance then causes imagination to go into overdrive so the person begins experiencing things that are not real in this or in the spiritual world.
Has anyone noticed that quite often, people who are genuinely able from a clairvoyant/psychic point of view are also very often at least slightly off balance mentally? I have never been diagnosed with a mental illness, nor shown any symptoms (at least, none that other 'mentally well' people don't also experience). None-the-less, I have had definite spiritual experiences, and at other times what I have thought might be a premonition has turned out just to be imagination.
Please, everyone who reads this, believe that I am not Bible bashing here, as although I believe in God Almighty and in Jesus Christ, I do not swallow the whole Bible. I trust the four Gospels - especially Matthew which was apparently the only book written by the Disciple of that name, and of course the Ten Commandments - although of course we all break a few of these at times. This is where the forgiveness of God through Jesus Christ comes in.
However, I also know I have lived before, in other bodies. The memories are rather similar to those of my life now. Bits and pieces of memories from long ago, never any life in it's entirety. I have also discovered that not only Hindus and Buddhists believe in re-incarnation, but so do the Druz of Lebanon, and a thousand or so years ago so did many Jews and Christians. The belief was proclaimed a heresy punishable by death by the emperor Augustus, as it was clear that those who believed in re-incarnation did not fear death the way non-believers did, and so believers were not afraid to die in battle. Hence, the need of Rome to extinguish the belief in re-incarnation.
Anyway, to continue, at one time I was physically paralysed, even my tongue so I was unable to ask my then boyfriend, who was next to me, for help. I was not particularly brought up as a Christian but had gone to church and had good experiences through this during my early to mid-teens, and all I could do was think "Jesus save me, Jesus please get it out of me" (I had definitely felt something climb inside me - for warmth, I think). After a few minutes of mentally praying for help, I felt whatever it was literally sit up and climb out of me again. This was absolutely not sleep paralyses, as I had that a couple of times since and it was nowhere near the same sort of experience.
Before that, when I was 14 years old I had a real premonition of a plane breaking in two whilst in flight, and somehow knew it would happen within three days. I told my father, who asked if perhaps I could 'find out' more about it, even if it was just the airline, maybe even the flight so it might be possible to tell someone in authority and perhaps stop it happening. After much prayer there was still nothing more, and then my father decided that maybe it was just as well, since if there were anything suspicious about the plane breaking up the authorities might think we knew something about it, or knew who was responsible. After this, after three days, it was on the news. A plane had broken up in mid-air.
I cried torrents of tears, of anger. Several times I shouted at God. Why had he let me see something so horrid and not let me know how to stop it? Then, I realised. Not everything comes from God. So I prayed again, and said sorry to Him, and that I realised it wouldn't have been from Him. I also asked Him to please protect me from seeing anything more that I couldn't stop, or be able to see how to stop. From that day to this He has honoured my prayer. I am now almost 55 yrs old, so that was about 41 years ago. One prayer, answered for life.
These are only two examples of real spiritual experiences I have had, but I have also had a very few false experiences which were clearly down to imagination.
I would guess that if a person were more spiritually sensitive than me, they may experience more of both real and false.
Going from my own experience, I would only say that it is important to remember that God and Jesus are about love, not ever about hurting oneself or others, and it is always possible to ask the Lord Jesus or our Heavenly Father to protect us spiritually.
For anyone who would ask, if God exists why is there so much evil in the world? The answer is explained again and again in the Bible...."I am not of this world" says God; "my world is not your world" God Said, and God said "I am spirit. I am not of this world". I think we have been taught by religion to expect too much of God in the physical world. Not that he hasn't be known to be able to reach out and help physically sometimes, but clearly his domain is spiritual and it is ultimately the well-being of our spirits he is most highly concerned with.
Even in the Bible, there is a distinction between 'true and false' spiritual experiences. Thus, my reasons for believing that more sensitive people can be so thrown by the true spiritual that they also become subject to the false. If it only takes two weeks for the brain to begin burning new nerve paths to BEGIN to accommodate a new habit, or BEGIN to lose an old habit, then of course real experiences and false experiences that cause confusion can cause chemical and physical changes in the brain that may be diagnosed as mental illness.
This is not to say that some people are not mentally ill rather that psychic, as anyone can become ill in the body or mind just through genetics and/or through traumatic events in their lives. However, I believe that SOME sufferers are genuinely psychic, and their illness is a result of the confusion between the true and falso in spiritual experiences.
Maybe others have another point of view?