Midazolam is a benzodiazepine commonly used for conscious sedation in dentistry.This paper reports a state of unconsciousness in a 14-year-old girl after administration of midazolam sedation for dental treatment, which was not reversible with flumazenil.The patient remained in an Intensive Care Unit for two days, unresponsive to any stimulus. A range of tests were inconclusive, but the diagnosis of an unusual reaction to midazolam was made. The patient fully recovered and was discharged from hospital after 6 days. A referral to a sleeping disorder clinic was made to investigate the patient's sleeping patterns.This paper highlights the importance of sedation being provided by an appropriately trained team.