conk out vs go to sleep

conk out

verb
  • to die 

  • to stop functioning 

  • to fall fast asleep; to sleep soundly 

go to sleep

verb
  • To die. 

  • To be affected by paresthesia; to go numb. 

  • To fall asleep. 

How often have the words conk out and go to sleep occurred in a corpus of books? (source: Google Ngram Viewer )