Doze off
Definition 1 of 1
Pro Tip 1/3Unintentional Act
Doze off happens without trying and often when you're supposed to be awake. 
I didn't mean to, but I started to doze off during the long drive.
Pro Tip 2/3Brief Sleep
Dozing off refers to a light, short sleep, not a deep or long slumber. 
During the movie, she just briefly dozed off.
Pro Tip 3/3Common Scenarios
Often used to describe situations where it's not ideal to sleep, like meetings or lectures. 
He had a hard time staying awake and dozed off in the workshop.