When Lygia Dunsworth was sedated, intubated and strapped down in the intensive care unit at a Fort Worth hospital, she was racked by paranoid hallucinations:Outside her window, she saw helicopters evacuating patients from an impending tornado, leaving her behind. Nurses plotted to toss her into rough lake waters. She hallucinated an escape from the I.C.U. — she ducked into a food freezer, only to find herself surrounded by body parts.Mrs. Dunsworth, who had been gravely ill from abdominal infections and surgeries, eventually recovered physically. But for several years, her stay in intensive care tormented her. She had short-term memory loss and difficulty sleeping. She would not go into the ocean or a lake. She was terrified to fly or even travel alone.Nor would she talk about it. “Either people think you’re crazy or you scare them,” said Mrs. Dunsworth, 54, a registered nurse in the Dallas-Fort Worth area. In fact, she was having symptoms associated with post-traumatic stress disorder.