Hypnosis is used to control physiologic changes that are thought to be involuntary. Hypnotized patients have, however, been able to control sympathetic tone, vasoconstriction, and vasodilation, heart rate, and muscle tone.7 It has been compared with biofeedback because patients are trained to voluntarily control these mechanisms. Biofeedback uses an external method of feedback whereas hypnosis uses an internal control from the patient.