fairy tale vs figment of one's imagination

fairy tale

noun
  • A story presented as true that is not believable. 

  • A delightful and ideal situation of a kind attained by very few. 

  • A folktale featuring fairies or similar fantasy characters. 

figment of one's imagination

noun
  • A product of the imagination. 

How often have the words fairy tale and figment of one's imagination occurred in a corpus of books? (source: Google Ngram Viewer )