other side vs retrogression

other side

noun
  • The afterlife, as a supernatural realm inhabited by spirits of deceased people. 

  • Used other than figuratively or idiomatically: see other, side. 

retrogression

noun
  • A return to a less complex condition. 

  • A deterioration or decline to a previous state. 

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