break down vs lose the plot

break down

verb
  • To cease to function. (others) 

  • To demolish, to pull down. (intentionally) 

  • To divide into parts to give more details, to provide a more indepth analysis of. 

  • To (cause to) decay, to decompose. 

  • To stop functioning. (machine, computer, vehicle) 

  • To fail, especially socially or for political reasons. 

  • To give in, relent, concede, or surrender. 

  • To render or to become weak and ineffective. 

  • To digest. 

  • To render or to become unstable due to stress, to collapse physically or mentally. 

  • To collapse, physically or in structure. (unexpectedly) 

lose the plot

verb
  • To cease to behave in a consistent and/or rational manner. 

  • To lose sight of an important objective or principle; to act contrarily to one's own interests through concentrating on relatively unimportant matters. 

  • Used other than figuratively or idiomatically: see lose, plot. 

How often have the words break down and lose the plot occurred in a corpus of books? (source: Google Ngram Viewer )