lunatic vs round the bend

lunatic

noun

  • An insane person. 

adj

  • Crazed, mad, insane, demented. 

round the bend

prep

  • Crazy, mad or insane. 

  • Close to or in close proximity to another location. 

How often have the words lunatic and round the bend occurred in a corpus of books? (source: Google Ngram Viewer )