fall asleep vs sleep in

fall asleep

verb
  • To pass from a state of wakefulness into sleep. 

  • To be affected by paresthesia; to go numb. 

  • To die (often seen on gravestones). 

sleep in

verb
  • Used other than figuratively or idiomatically: see sleep, in. 

  • To sleep late; to go on sleeping past one's customary or planned hour. 

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