This was not done only to cure illness, but also as a purification rite before religious ceremonies, before a battle, or when the person hoped for a vision.
When ordered by the shaman for curing a disease, rites and incantations, drumming, and singing by the people would add the atmosphere of magic or miracle. Herbs might be placed on the hot stones as well.
Until the discovery of antibiotics, a modification of the practice was held in high esteem by most medical doctors. Anybody over forty is almost sure to have experienced the discomfort of profuse sweating to “open the pores”. The effect was brought on by certain drugs, aspirin, or hot lemonade, with or without rum or brandy, and piles of bedclothes over heated bricks or hot water bottles. Oddly enough, in many cases, it did serve to “break the fever” or “loosen a cold” or ease acute stiffness and pain following severe exercise. I can still remember that nightmares frequently accompanied the uneasy sleep that followed the ordeal. “Vision” was not quite the word for it, but the concept is very much the same. Whether the practice did have some physical value, or whether it only gave the patient a psychological lift is not known. Those who are devotees of sauna baths are in the best position to give an opinion based on experience