It's called psychosomatic illness. You can develop all the symptoms without actually having the disease. That's different to hypochondria where somebody basically imagines they are ill when they're not. Psychosomatic symptoms are real, but their genesis is in the mind.
There was a study done on this during WW2 and it was learned that malingerers (that is, people who were faking ailments to get out of combat) often developed the problems they were faking.
We also had a case in Oz of a prominent actor who played the part of a loser in a very successful TV series who developed depression, almost certainly as a result. He was just too good an actor and threw himself into the role too well.
Sure, people "psych" themselves into feeling ill all the time. Usually it is the stress and worry making you feel sick/tired/weak but in extreme cases people can have heart palpitations, break out in hives and exhibit other more serious symptoms, this is called "psychosomatic illness"
yes but that's what you call a hypochondriac which is someone who believes there is always something different wrong with them. there is also another name that I can't remember that means if you are reading different symptoms you begin to imagine you have them