formication vs gnawing

formication

noun
  • An abnormal skin sensation similar to that of insects crawling over or within the skin; a tactile hallucination involving such a sensation. A common side-effect of substance abuse, it can also be experienced with high fever, menopause, skin cancer, diabetic neuropathy, or herpes zoster. 

gnawing

noun
  • A sensation of being gnawed. 

  • The process by which something is gnawed. 

adj
  • severe or intense 

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