spring fever vs unconcerned

spring fever

noun
  • A feeling of invigoration and restlessness associated with the arrival of the warm weather and renewal of nature in the spring season. 

  • A feeling of laziness or listlessness associated with the arrival of the warm, comfortable weather of the spring season. 

unconcerned

adj
  • Not anxious, apprehensive, or worried. 

  • Having no involvement. 

  • Indifferent and having no interest; aloof. 

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