freeze up vs lose nerve

freeze up

verb
  • To become cold and formal in demeanour. 

  • (of machines and software) To come to a sudden halt, stop working (functioning). 

  • To be adversely affected by ice, and not function. 

  • (of people and other animals) To stop or be stopped due to attentiveness, fear, surprise, etc. 

lose nerve

How often have the words freeze up and lose nerve occurred in a corpus of books? (source: Google Ngram Viewer )