Nod Off Meaning

(idiomatic) To fall asleep, especially while in a seated position or in inappropriate circumstances.

Example: 1857, William Makepeace Thackeray, The Virginians, ch. 53,
  The old lady nodded off to sleep many times during the narration, only waking up when George paused, saying it was most interesting.
1914, Robert Frost, "The Death of the Hired Man," lines 41-44,
  I dragged him to the house,
  And gave him tea and tried to make him smoke.
  I tried to make him talk about his travels.
  Nothing would do: he just kept nodding off.
2008, Ingfei Chen, "A Leap Forward, but Hurdles Remain in Narcolepsy," New York Times, 15 Feb. (retrieved 16 July 2008),
  All patients struggle against daytime drowsiness and nod off at inopportune moments.