A 55-year-old patient addressed a prostodontic clinic to have a denture made. During preparation of the 44 and 47 teeth for crown installation the patient became unwell: he developed vertigo, nausea, tinnitus, blurred vision, dyspnea. Unconsciousness followed, the pupils were dilated, heart rate was weak. After 1 minute the patient’s condition improved. What condition occurred in the patient?