If he started to fall asleep, the tool would fall from his hand.

VOA: special.2009.03.18

The slow movement made Paul fall asleep.

VOA: special.2009.04.11

"Three or four hours before I could fall asleep. I wake up three o'clock in the morning with the same stuff on my mind, tossing and turning.

VOA: standard.2010.05.04