keel over vs plummet

keel over

verb
  • To collapse in a faint; to black out, to swoon. 

  • To die. 

  • Of a vessel: to roll so far on its side that it cannot recover; to capsize or turn turtle. 

plummet

verb
  • To drop swiftly, in a direct manner; to fall quickly. 

noun
  • A violent or dramatic fall. 

  • A decline; a fall; a drop. 

How often have the words keel over and plummet occurred in a corpus of books? (source: Google Ngram Viewer )