crack up vs get flustered

crack up

verb
  • To cause to laugh heartily. 

  • To become insane; to suffer a mental breakdown. 

  • To crash an aircraft or automobile. 

  • To laugh heartily. 

  • To cry up; to extol. 

adj
  • Funny; hilarious 

get flustered

How often have the words crack up and get flustered occurred in a corpus of books? (source: Google Ngram Viewer )