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One in every 19,000 patients wakes up at some point during surgery, a big UK study of awareness during surgery has concluded. Episodes of awareness are usually short - but as many as 40 percent of those studied reported psychological damage including Post Traumatic Stress Disorder as a result. A consultant anaesthetist explains how this can happen, but first we hear from a woman with first-hand experience – 50-year-old Tracey Snelling. In 2010, she was having an operation on her nose, for sinus problems.

(Photo: A surgeon and his team perform a keyhole operation. Credit: Christopher Furlong / Getty Images)