Original SDMB thread Can one ever be driven insane without underlying mental disease?
Not only can it happen to "anyone" (or at least to a great many people under the right circumstances, and that would include me), there is no mechanism for determining whether or not the person to whom it happened has, or does not have, an "underlying" mental disease.
The docs don't test your blood for serum levels of schizophrenerase. All diagnoses are made on the basis of observed behavior and behavior to which the subject (or other folks) testify. Therefore the word "underlying" simply doesn't make any sense in this context. If it's "underlying" it can't be detected; if it is detectable, the "insane" symptoms are not distinguishable from something else that constitute the "disease itself".
The entire construct "mental illness", in the medical-model sense of being an actual somatic condition of the brain, a physical neuro disorder manifesting itself as the symptoms that land one a psychiatric diagnosis, is drawn from induction and (::checks forum:: IMHO, assumption, i.e., in the absence of a preexisting hypothesis that mental illness existed, all the physical evidence found to date and concatenated into one research report would not tend to cause folks to conclude that any definitive phenomenon had been described there.