nightmare vs sleeping

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. 

sleeping

noun
  • The state of being asleep, or an instance of this. 

adj
  • Asleep. 

  • Used for sleep; used to produce sleep. 

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