hibernation vs sack time

hibernation

noun
  • A hypothetical state of minimum power consumption, inactivity and metabolic depression in humans during long space flights. 

  • A state of minimum power consumption, inactivity and metabolic depression in some animals during winter. 

  • A standby state which conserves power by writing the contents of the memory to disk and completely power off the computer, in order that one will resume the session from the disk. 

sack time

noun
  • Time spent sleeping. 

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