h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

This is a question for anyone who has either a)worked as a caregiver in the field of mental health, b)researched psychosis and paranoid delusions, delusions of granduer etc or c)either qualified in psychiatry/psychology or taken far to many illicit mind altering substances and experienced at least the belief of involvment in most of the above.
Why is it that so many people from so many different backgrounds with such a diverse range of life experience when suffering from psychosis whether drug induced or a more natural chemical problem all seem to experience such similar episodes? I became interested in this a few years ago when someone i know took substantial quantities of mushrooms and ended up under the care of mental health with some very unusual ideas about life the universe and everything. After much reading of accounts of other psychotic/recovered peoples from both different nations/enviroments and time periods i started to see alot of very similar accounts of what was imagined to be happening in the lives of these people. I have had little luck in finding a clinical test or report as to why this may be the case?
and even if you cannot help enlighten me as to why this is the case perhaps you have an interesting account of the often tragic but more often hilarious behaviour/beliefs of our felllow humans that sincerely believe things most of us find unacceptable.