at one's wits' end vs nonplussed

at one's wits' end

nonplussed

adj

  • Unsure how to act or respond; bewildered, perplexed. 

  • Unaffected, unfazed; unimpressed. 

How often have the words at one's wits' end and nonplussed occurred in a corpus of books? (source: Google Ngram Viewer )