There seems to be a surface similarity of some varieties of insanity and shamanism. In some ways it seems to be a matter of control. An example would be schizophrenia. In the case of a schizophrenic, the sufferer typically does what the voices tell him to do; in the case of a shaman, the affected person has power over the voices. Whether these similarities hold up to the flashlight of scrutiny or evanesce into the swamp of coincidence may never be known by me. The premier work on the subject is Shamanism by Mircea Eliade and I have never been able to make it past page 3.