I have recently stumbled across some interesting entries on the blog of Kenneth A. Nakdimen, M.D. The first (19 February 2019) asks, "Do Fiction Writers Have Alternate Personalities," and cites a study by Marjorie Taylor: http://multiplewriters.blogspot.com/. The same site also has a five-part series (through 20 February 2019) on Aldous Huxley's "Personality and the Discontinuity of the Mind."
On a related and not altogether dissimilar note, I have had dreams in iambic pentameter. Indeed, the entire story-line of my one-act version of Hamlet came to me in that manner, along with some of the verse. Perhaps more intriguing is the vast amount of musical material that his been similarly "dictated" to me during dreams. Of course, I do not believe this is a manifestation of multiple personality disorder. . . .