Charles II of Spain: Court Exorcism

Charles II had many physical (and likely mental) ailments due to the Hapsburg family's long history of inbreeding, as they believed that marrying within the family would keep the royal bloodline "pure." Genetics were not well understood and officials at the time attributed his ailments to spiritual affliction. Priests and court physicians were called to perform various exorcism ceremonies, which had some level of placebo effect on him, but only weakened him further in the long run.