doss down vs drop off

doss down

verb
  • To sleep on someone's sofa or floor because there is no bed spare. 

drop off

verb
  • To fall asleep. 

  • To fall. 

  • To deliver; to deposit or leave; to allow passengers to alight. 

  • To lessen or reduce. 

How often have the words doss down and drop off occurred in a corpus of books? (source: Google Ngram Viewer )