[pengaru]

Automobile passenger compartments are vented, otherwise there'd be problematic pressure spikes on door/hatch closures. You're not getting deprived of oxygen sleeping in a vehicle.

[feet]

What is the rate of air exchange in a closed passenger compartment of a vehicle that is not running?

Likewise, what is the rate of CO2 production from an average sedentary human?

On top of that, what is the rate of combustion byproduct production from burning plant matter in a closed passenger compartment?