Psychologist Robert Lindner's 1955 book The Fifty-Minute Hour details the case of a man who believed he was "living part of the time in another world—on another planet." And many people now believe this famous case study was actually Norstrilia author Paul Linebarger, aka Cordwainer Smith.
Over at The Alantic, there's a fascinating rundown of the case of Kirk Allen, the man who believed he lived on other worlds — and the theories that tie him to Linebarger. It's also a great celebration of his life and his writing Ted Gioa writes:
Brian Aldiss first reported the possible linkage between Smith and Kirk Allen—the name used by Lindner for his patient—in 1973, and subsequent research by Alan Elms and Lee Weinstein has tended to substantiate, although not definitely prove, the connection.
According to Lindner, his patient first began experiencing a strange feeling while reading fanciful adventure novels during his youth. "In some weird and inexplicable way I knew that what I was reading was my biography [emphasis Lindner's]. Nothing in these books was unfamiliar to me: I recognized everything... My everyday life began to recede at this point. In fact, it became fiction—and, as it did, the books became my reality." At the further stage of this "psychosis," the patient "filled in the spaces" between the written stories with "fantasy 'recollections.'"
There's much more, including some great discussion of the themes and great merits of Smith's stories and his one novel — and a comment ostensibly from one of Smith's children — at the link. [The Atlantic]