The thing is, when a car hits water, it is usually in a violent way where I would imagine people would be momentarily stunned. By that time, the water pressure

The thing is, when a car hits water, it is usually in a violent way where I would imagine people would be momentarily stunned. By that time, the water pressure outside would be too high for them to open the door. Breaking the window is a bit hard to do as well for most people in that situation. Breakout window tools are great, but most people leave their tools in the trunk. This is where the controlled breathing is vital. I have not been in this situation, but I have been in drowning situations where I have helped someone in the ocean. I took quick, deep breaths and it helped me while I was underneath the water searching. When I was a kid, I took swimming lessons, and the first thing the trainer talked about was controlled breathing. Before we even started swimming around, he would make us stay still while taking deep breaths. Try it anywhere and you will see how your body reacts to it afterwards.