Scientific/Psychological Treatise; "Autobiography"
At its most basic level, The Interpretation of Dreams is a scholarly text. As a practicing psychoanalyst, Freud intended the book to contribute to—and maybe even revolutionize—contemporary psychological and psychoanalytic practice. Eventually, it did. As Freud had hoped, The Interpretation of Dreams changed the way that turn-of-the-century therapists understood their patients' psychical and physiological symptoms and disorders.
That said, The Interpretation of Dreams has also been called an autobiography—or, as one scholar puts it, a "disguised autobiography" (source). Because Freud's interpretations of his own dreams reveal intimate information about his childhood, marriage, and professional life, the book not only made waves in medical circles, but it also provided Freud's readers with a snapshot of the author's own inner life.
How's that for a genre-crossing narrative?