sleep over vs slumber

sleep over

verb
  • To spend the night as a guest in someone's home. 

slumber

verb
  • To be in a very light state of sleep, almost awake. 

  • To be inactive or negligent. 

noun
  • A state of ignorance or inaction. 

  • The snooze button on an alarm clock. 

  • A very light state of sleep, almost awake. 

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