drop off
phrasal verb with drop verb uk/drɒp/ us/drɑːp/ -pp-
(SLEEP)
入睡
to start to sleep
(DECREASE)
减少，下降
If the amount, number, or quality of something drops off, it becomes less.
The demand for mobile phones shows no signs of dropping off. 人们对手机的需求并未出现下降的迹象。