delusion vs flight of imagination

delusion

noun
  • A false belief that is resistant to confrontation with actual facts. 

  • A fixed, false belief, that will not change, despite evidence to the contrary. 

  • The state of being deluded or misled, or process of deluding somebody. 

  • That which is falsely or delusively believed or propagated; false belief; error in belief. 

flight of imagination

How often have the words delusion and flight of imagination occurred in a corpus of books? (source: Google Ngram Viewer )