neurasthenia vs sloth

neurasthenia

noun
  • An ill-defined medical condition characterized by lassitude, fatigue, headache, and irritability, associated chiefly with emotional disturbance. 

sloth

noun
  • Laziness; slowness in the mindset; disinclination to action or labour. 

  • A herbivorous, arboreal South American mammal of the families Megalonychidae and Bradypodidae, noted for its slowness and inactivity. 

  • A collective term for a group of bears. 

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