We take it for granted until it doesn't happen the way it always has. We notice it when others are struggling with it. And it's one of the signs that something is seriously wrong.
Take a minute and just breathe. Notice how it feels. How your body moves and changes with the inhale and exhale. Notice if you can feel the temperature change in your throat or around your nostrils. Notice if there are hesitations or hitches as you go through the process. Hold the breath at the top and notice when you need to exhale. Try to match the inhale length with the exhale.
Dr Nedley encourages us to breathe deeply, taking only 3-6 breaths per minutes for 30-45 minutes per day. It doesn't have to be all at once during the day, maybe it is when you are driving, or even stopped at stop lights. Just take a minute and breath.