sluggishness vs somnolence

sluggishness

noun
  • The property of being sluggish, unable or unwilling to act quickly. 

  • The state of economic decline, inactivity, slow or subnormal growth. 

somnolence

noun
  • A state of drowsiness or sleepiness. 

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