From Longman Dictionary of Contemporary Englishdrop off phrasal verb1SLEEPto begin to sleepShe kept dropping off at her desk.I must have dropped off to sleep.2 drop somebody/something ↔ off to take someone or something to a place by car and leave them there on your way to another placeI’ll drop you off on my way home.3LESSto fall to a lowerlevel or amountThe number of graduates going into teaching has dropped off sharply. →drop→ See Verb table
Examples from the Corpus
drop off• She kept dropping off for a few minutes, before waking with a start.• At around 12.30, she did eventually drop off for an hour or so.• Janir had dropped off to sleep on the living roomcouch.dropped off to sleep• Eventually we dropped off to sleep.• Gillian sat in the back and soon dropped off to sleep.• I must have dropped off to sleep.• On the drive back to St Petersburg the girl once again dropped off to sleep.• Mrs Wright had dropped off to sleep again, making a kind of whistling noise through her mouth.• The babydropped off to sleep in the car.• I had barely dropped off to sleep when I was suddenly awakenedbsharp abdominal pains.From Longman Business Dictionarydrop off (also drop away) phrasal verb [intransitive]MARKETINGto become lower in level or amountSales have dropped off in recent months.With the strong pound, tourism has dropped off. → see alsodrop-off →drop→ See Verb table
drop-offˈdrop-off noun [countable]1if there is a drop-off in the amount, level, or number of something, it goes down or becomes lessThere has been a drop-off in tourism this year.temporary drop-offs in sales2TRANSPORTa delivery, or the place where something is delivered toA truckload carrier takes a full cargo from one point to another, without any intervening pickups or drop-offs.