enervation vs lethargy

enervation

noun
  • State of being enervated; debility. 

  • Act of enervating; debilitation. 

lethargy

noun
  • A state of extreme torpor or apathy, especially with lack of emotion, energy or enthusiasm; (loosely) sluggishness, laziness. 

  • A condition characterized by extreme fatigue or drowsiness, deep unresponsiveness, or prolonged sleep patterns. 

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