When a patient is given general anaesthesia, how unconscious do they become? On the face of it, this seems to be a silly question. Patients do not respond to extremely noxious stimuli, and almost all have no memories of the surgery and are very happy with their experience of anaesthesia. Nonetheless there is a disquieting body of evidence hinting at the occurrence of—often covert—conscious experiences whilst under apparently adequate anaesthesia.¹ General anaesthetic drugs usually cause amnesia, so studies that rely on postoperative recall will almost certainly be an underestimate of the true incidence.