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Take a look into the history of psychology and you may be able to find some information that is helpful to you. Many exorcisms were performed on people thought to be possessed by a demon or the devil himself when in fact, these people actually suffered from mental disorders. The interesting thing is that sometimes they actually got better after the exorcism even though nothing had really been done to address the mental condition. Eventually, they usually relapsed after a short period. People with physical ailments like seizures or disfigurements were also thought to be possessed.

Look up the name Anneliese Michel which is a very interesting modern case although much about it has been fictionalized so you have to be careful to only get the facts. Also take a look into "spiritual healers".

Or how about taking a look at anxiety attacks? This is a big one and would be easy to work with. As a nurse, you'll deal with it many times. Is it physical or psychological? Many people experiencing an anxiety attack for the first time will rush to the ER thinking they are having a heart attack. A person experiencing an anxiety attack will have a very physical and serious reaction but the root cause is psychological.