A literal failure of imagination

 In my dream this morning, there was very tall young man threatening to beat me up. The interesting thing about this was that when I asked him why he became completely unintelligible, as in barely making human sounds, let alone speaking a language.

My interpretation of this is that it indicates a literal failure of my imagination to produce a response to my question: like my imagination had brought us to a certain point in the dream, then it didn't know how to proceed, and went haywire.

Something similar to this, I would say, is when you've dreamed that you've written something really wonderful but when you strain to see what is exactly on the page you can't identify a single word. Your imagination isn't able to come up with it and your wonderful writing is revealed to be a mere actor's prop in the staging of the dream.