There's more to breathing than your choice of orifice.
Sit up, stand, or lay flat. Take a deep breath. As deep as you can. Do it a few times.
Did your stomach or your chest expand? Does your neck tense up as you inhale? Did your shoulders move apart and back? These are all things to consider when thinking about breathing. You SHOULD breathe in through your nose, keep your neck relaxed, and your stomach should expand, as your diaphragm (muscle under your lungs) drops down to fill your lungs with air. If your chest expands, then you're using your chest muscles to breathe. Same story with shoulders. Tensing your neck is dumb, but some people do it. Trained actors and singers can often control their breathing to the point of using their back muscles, or ribs. We call that breathing into one's back, or ribs, respectively.
Breathing: it's complicated.
Again Rebbay, how do you breathe?