deteriorate vs fall off

deteriorate

verb
  • To make worse; to make inferior in quality or value; to impair. 

  • To grow worse; to be impaired in quality; to degenerate. 

fall off

verb
  • To become detached or to drop from. 

  • To diminish in size, value, etc. 

  • To fall into sin; stray. 

  • To change the direction of the sail so as to point in a direction that is more down wind; to bring the bow leeward. 

How often have the words deteriorate and fall off occurred in a corpus of books? (source: Google Ngram Viewer )