This article presents the third molar removal in a highly hypnotizable patient, who had been successfully submitted to oral surgery with hypnosis as stand-alone anesthesia in previous sessions. Unexpectedly, hypnosis initially failed, as a result of a nocebo response due to a previous dentist's bad communication; two complaints made by the patient were associated with increased sympathetic activity (as defined by increased heart rate and electrodermal activity and decreased heart rate variability). After deepening of hypnosis, the patient achieved a full hypnotic analgesia allowing for a successful conclusion of the intervention, an event associated with decreased heart rate, electrodermal activity, and increased heart rate variability. Hence, the initial failure was paralleled by a decreased parasympathetic activity and increased sympathetic activity, while hypnotic analgesia was associated with the opposite pattern. The patient's postoperative report indicated that the initial failure of hypnosis depended on a strong nocebo effect because of a previous dentist distrusting hypnosis and persuading her that it was not enough to face a third molar removal.