The average person breathes at least 20,000 times per day. Our amazing brain controls this so that we do not have to consciously think about every breath we take. This allows us to be able to focus on the things we actually want and need to do each day. We are meant to breathe primarily through our noses. When, because of postural and/or structural changes, we start shifting toward mouth breathing, we can develop many problems. Some of these issues include forward head position, difficulty sleeping, and overall breathing weakness.
As noted in this glocal.com slide several things can go wrong with mouth breathing: