I hope this helps in understanding some beliefs. http://altmed.creighton.edu/AmericanIndianMed/
The meaning of the term medicine to an American Indian is quite different from that which is ordinarily held by modern societies. To most American Indians, medicine signifies an array of ideas and concepts rather than remedies and treatment alone. There is no separation between religion and medicine in tribal culture and healing ceremonies are an integral part of the community experience. To the American Indian, the natural or correct state of all things, including man, is harmony. Far from being dominant over nature, man is seen as interdependent with other living beings and physical forces. All thinking is grounded in relationships. More emphasis is given to the connectedness of one thing to another than to the individual thing itself. To maintain a correct or natural relationship is to be in harmony. The universe is a complex matrix of interdependence. There is a proper set of relationships for each being, a proper existing in harmony with the universe.
George Bird Grinnell, who was intimately associated with northern Plains tribes, has written:
“All these things which we speak of as medicine the Indian calls mysterious, and when he calls them mysterious this only means that they are beyond his power to account for… He whom we call a medicine man may be called a doctor, a healer of diseases; or if he is a worker of magic, he is a mystery man. All Indian languages have words which are the equivalent of our word medicine, sometimes with curative properties; but the Indian’s translation of “medicine,” used in the sense of magical or supernatural, would be mysterious, inexplicable, unaccountable.
Tribal cultures interpret disease and human suffering as disharmony. An individual suffers because in some way he or she has fallen out of harmony. The person who does not feel well has gotten out of phase with the correct relationships. Their medical theory arises from the reasoning that the medicine man can control the forces of nature and hence make disease yield to his personal effects. Consequentially, curative agents are medicine, but only one type of medicine, and then only when it is association with prescribed rites. The medicine man is entrusted with ceremonies connected with birth and death, magical ceremonies, and the perpetuation of tribal lore. He is not only the primitive doctor, but he is the diviner, the rainmaker, the soothsayer, the prophet, the priest, and in some instances the chief. Some of the better-known American Indian chiefs were in fact medicine men: Sitting Bull, Geronimo, and Cochise.