It's rude to fall asleep in public.
Liz is on the bus getting a ride home, and she is very drowsy from working all day.
Liz wants to get some sleep soon.
Liz makes herself stay up until she gets back home and sleeps right away.
Liz allows herself to fall asleep while still riding on the bus.
The other people riding the bus have a peaceful ride home.
The other passengers are disturbed by Liz snoring and leaning over her spot.