A Vision: The Inspiration of the Poet (Elisha in the Chamber on the Wall)circa 1819-20. Tate Britain.
A representation of Blake's imagination when being inspired by his angels. Interesting that the (divine) imagination is represented by a room within a room in much the same way as St. Jerome's study. El Greco had a more organic interpretation of spaces within dreams - Philip II's Dream 1580
In terms of representing dreams, the movie Inception has inspired many infographics to chart the layers which are a sort of time/dream matrix