As someone who has a CC permit, let me explain how I carry.
I also have a holster that clips inside my pants/skirt, and is a “back” holster. That means I carry it, just behind my hip. I do not carry in the “back.”
First, no one carries back by their spine. Think about it. If you sit down, the weapon would be pressing against your spine. That would be painful. Also, you would have to reach all the way back there if you ever need to draw your weapon.
So, you (the general public, you) carry at your back, but toward the side. And if you are on the ground, the weapon would either push forward, or you would push your body up off of the ground. (It would be like lying on a brick.)
So, if I were to carry and I somehow end up on my back, my gun wouldn’t be under me.