Three fantasy titles of all shapes and sizes - Marion Zimmer Bradley's The Falcons of Narabedla, Greg James' Under A Colder Sun and Alex Marshall's A Crown for Cold Silver.
Marion Zimmer Bradley's The Falcons of Narabedla (1957)
Mike does radio things in a Government Lab. Electricity happens, and, ker-wham, he's mind-ported to Narabedla, Last of the Rainbow Cities. Mike's consciousness rests in the body of Adric, one of Naradebla's arrogant ruling class. Adric's mind isn't totally gone, but sort of repressed, helping Mike/Adric get dressed and occasionally resurfacing in a plot-pushing kind of way.
M'Adric is thrown in at the deep end. Fortunately, there are a lot of people around who are happy to elaborate on Narabedla's history, culture and current events. M'Adric learns that the rulers of Narabedla all have a captive Dreamer under their thrall - a powerful, wish-granting psychic - more djinn than mortal. Adric, in his pre-Mike days, seems to have done something naughty and loosed one of the Dreamers. Now the entire system is under threat. Will there be a revolution? Should there be a revolution? Plots within plots, betrayals within betrayals - including Mike and Adric scheming against one another. From within the same body!