In my opinion, it is definitely how receptive or believing the mind of the "victim" is to this stuff. If you think it can happen -- it probably will, in one form or another. Mind over matter.
Years ago when I was younger, I got really drunk one night. Being a weekday I had to work the next day (mechanical job). I went into work with a massive hangover and just mentioned that it seemed warm in the shop. There was another guy there who was a real psycho-somatic type. When I realized I had caught his attention, I thought I might have some fun.
I asked him if he thought it was warm. He said not really but looked concerned. Then I told him I thought it was cool and he tentatively agreed. This went on for a little while, me telling him it seemed warm and then a little later telling him it seemed cold and back-and-forth like this for a while. I also interspersed my temperature complaints with a headache and such.
After about an hour this poor sap went home sick! He had gotten sick with chills and had to go home because he (thought he had...) the flu or something worse. This guy got a case of chills and self-inflicted flu ... from my hangover and the power of suggestion!
Needless to say the others in the shop thought it outrageously funny and never let this guy live it down. Yep, the mind is a powerful thing!
Robert