plop oneself vs sit up

plop oneself

sit up

verb
  • To not go to bed (notionally remaining in a sitting position). 

  • To show sudden interest or surprise. 

  • To sit erect. 

  • For a young lady to open her house for several successive nights for any visitors who wish to pay their respects. 

  • To assume a sitting position from a position lying down. 

  • To bounce, especially to a comfortable height. 

How often have the words plop oneself and sit up occurred in a corpus of books? (source: Google Ngram Viewer )