It starts with whoever falls asleep first.
If they are the a snorer
it may lead to elbowing,
asking politely in an annoyed tone,
subtly manoeuvring a person, or simply holding their nose.
But then there is a dilemma,
where do you put your arms?
Do you risk having a dead arm in the morning?
Or accidentally hitting them in the face in your sleep? Because you obviously need to protect yourself from…