night hag vs nightmare

night hag

noun
  • a demon that gives rise to sleep paralysis 

nightmare

noun
  • A feeling of extreme anxiety or suffocation experienced during sleep; Sleep paralysis. 

  • Any bad, miserable, difficult or terrifying situation or experience that arouses anxiety, terror, agony or great displeasure. 

  • A very bad or frightening dream. 

verb
  • To have a nightmare. 

How often have the words night hag and nightmare occurred in a corpus of books? (source: Google Ngram Viewer )