No, you do not need to crack a window when you are sleeping in a car. Vehicles
are not air tight. When you are inside a car, air is continually circulating which generally leaves enough
oxygen inside to sustain your breathing. Keeping your truck window cracked while you are asleep can sometimes
lead to safety issues, as you don’t want to leave an opening large enough for someone to access the inside
of your car while you are asleep.