Following one of many suicide attempts and manic or depressive episodes, Sexton worked with therapist Dr. Martin Orne. He diagnosed her with what is now described as bipolar disorder, but his competence to do so is called into question by his early use of allegedly unsound psychotherapeutic techniques. During sessions with Anne Sexton he used hypnosis and sodium pentothal to recover supposedly repressed memories. During this process, he allegedly used suggestion to uncover memories of having been abused by her father.  This abuse was disputed in interviews with her mother and other relatives. Dr. Orne wrote that hypnosis in an adult frequently does not present accurate memories of childhood; instead, "adults under hypnosis are not literally reliving their early childhoods but presenting them through the prisms of adulthood." According to Dr. Orne, Anne Sexton was extremely suggestible and would mimic the symptoms of the patients around her in the mental hospitals to which she was committed. The Diane Middlebrook biography states that a separate personality named Elizabeth emerged in Sexton while under hypnosis. Dr. Orne did not encourage this development and subsequently this "alternate personality" disappeared. Dr. Orne eventually concluded that Anne Sexton was suffering from hysteria. During the writing of the Middlebrook biography, Linda Gray Sexton stated that she had been sexually assaulted by her mother.  In 1994, Linda Gray Sexton published her autobiography, Searching for Mercy Street: My Journey Back to My Mother, Anne Sexton, which includes her own accounts of the abuse.
Middlebrook published her controversial biography of Anne Sexton with the approval of Linda Gray Sexton, Anne's literary executor. For use in the biography, Dr. Orne had given Diane Middlebrook most of the tapes recording the therapy sessions between Orne and Anne Sexton. The use of these tapes was met with, as The New York Times put it, "thunderous condemnation." Middlebrook received the tapes after she had written a substantial amount of the first draft of Sexton's biography, and decided to start over. Although Linda Gray Sexton collaborated with the Middlebrook biography, other members of the Sexton family were divided over the book, publishing several editorials and op-ed pieces, in The New York Times and The New York Times Book Review.
Controversy continued with the posthumous public release of the tapes (which had been subject to doctor-patient confidentiality). They are said to reveal Sexton's inappropriate behavior with her daughter Linda, her physically violent behavior toward both her daughters, and her physical altercations with her husband.
Yet more controversy surrounded allegations that Anne Sexton had an affair with the therapist who replaced Dr. Orne in the 1960s. No action was taken to censure or discipline the second therapist. Dr. Orne considered the affair with the second therapist (given the pseudonym "Ollie Zweizung" by Middlebrook and Linda Sexton) to be the catalyst that eventually resulted in her suicide.