bed down vs go to sleep

bed down

verb
  • To lie down to sleep for the night, usually of livestock or machinery. 

  • To put an animal to rest for the night. 

go to sleep

verb
  • To fall asleep. 

  • To be affected by paresthesia; to go numb. 

  • To die. 

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