go to bed vs go to sleep

go to bed

verb
  • To lie down to sleep, put oneself in one's bed. 

  • Of a newspaper: to finish being prepared for printing. 

go to sleep

verb
  • To fall asleep. 

  • To be affected by paresthesia; to go numb. 

  • To die. 

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