mania vs mental instability

mania

noun
  • Dotcom mania was slow in coming to higher education, but now it has the venerable industry firmly in its grip. Since the launch early last year of Udacity and Coursera, two Silicon Valley start-ups offering free education through MOOCs, massive open online courses, the ivory towers of academia have been shaken to their foundations. 

  • The state of abnormally elevated or irritable mood, arousal, and/or energy levels. 

  • Violent derangement of mind; madness; insanity. 

  • Excessive or unreasonable desire; insane passion affecting one or many people; fanaticism. 

  • 2013-07-20, “The attack of the MOOCs”, in The Economist, volume 408, number 8845 

mental instability

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