While reading Kenneth Dewhurst's book Thomas Sydenham (1624-1689): His Life and Original Writings, (University of California Press, 1966) I ran across an amusing instance of what appeared to me to be a psychological treatment:
"Riding long journeys on horseback was one of Sydenham's favourite remedies ... After attending a … (wealthy patient) for several months without alleviating his symptoms, Sydenham frankly told him that he was unable to render any further service. But he added that a certain Dr. Robertson of Inverness had performed several remarkable cures in this particular malady. Armed with Sydenham's letter of introduction, the patient set out for Inverness where he lost no time in seeking Dr. Robertson. to his dismay he learned that there was no physician of that name in the city, nor had there ever been one in the memory of anyone there. Returning to London the gentleman vented his indignation of Sydenham for having him on such a long and fruitless journey. "Well," inquired Sydenham, "are you in any better health?"
"Yes, I am not quite well, but no thanks ty you."
"No," added Sydenham, "but you may thank Dr. Robertson for curing you. I wished to send you on a journey with some objective interest in view. I knew it would be of service to you; in going you had Dr. Robertson and his wonderful cures in contemplation, and in returning, you were equally engaged in thinking of scolding me." [pp. 53-4]
If anyone knows of other instances of the therapeutic effects of such deceptions, I would be interested in learning about them.