hydrophobia vs mental illness

hydrophobia

noun
  • A morbid fear of water; aquaphobia. 

  • An aversion to water, as a symptom of rabies; the disease of rabies itself. 

mental illness

noun
  • A mental disorder. 

  • The property of being mentally ill; mental disorders taken as a whole. 

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