drift_off
1. [ verb ] change from a waking to a sleeping state
Synonyms: fall_asleep drop_off nod_off flake_out doze_off drowse_off dope_off
Examples:

"he always falls asleep during lectures"

Related terms: wake_up zonk_out
Similar spelling:   driftwood
  driftfish
  drift_net
  drift_ice
  drift_away
  draft_copy
  drifter
  drift_apart
  draft_horse
  draft_board