lethargy vs weakness

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. 

weakness

noun
  • The condition of being weak. 

  • An inadequate quality; fault 

  • A special fondness or desire. 

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