inertness vs lassitude

inertness

noun
  • Lack of activity or exertion; habitual indisposition to action or motion 

  • Absence of the power of self-motion; inertia. 

  • Quality of being unreactive with other chemical compounds or elements. 

lassitude

noun
  • Lethargy or lack of energy; fatigue. 

  • Listlessness or languor. 

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