somnolence vs torpor

somnolence

noun
  • A state of drowsiness or sleepiness. 

torpor

noun
  • A state similar to hibernation characterised by energy-conserving, very deep sleep. 

  • A state of being inactive or stuporous. 

  • A state of apathy or lethargy. 

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