One day in 2009, twenty-four-old Susannah Cahalan woke up alone in a strange hospital room, strapped to her bed, under guard, and unable to move or speak. A wristband marked her as a "flight risk," and her medical records, chronicling a month-long hospital stay of which she had no memory at all, showed hallucinations, violence, and dangerous instability. Only weeks earlier, Susannah had been on the threshold of a new, adult life, a healthy, ambitious...