Carl sent in a link to a book called Alternative Worlds in Hollywood Cinema, which possibly has a section dedicated to Eternal Sunshine of the Spotless Mind. Says the book's summary, in part:

Alternative worlds in films such as The Wizard of Oz, It's a Wonderful Life, Donnie Darko and Eternal Sunshine of the Spotless Mind offer similarities and resonances to our world, but provide a way for filmmakers to address the human condition by forming a sincere and serious connection with everyday life.

...An illuminating new book explores the history, background and meaning of films that feature alternative worlds – films in which characters cross back and forth between another world and our own, which bring out correspondences and resonances between the worlds they depict.

... In each of the films discussed the flight from the real world results in characters having to face reality again, equipped with new knowledge and experience, enabling them to find a way of living there from that day on. (Source)

So if you're inclined to check that out... do check it out.