We breathe in three dimensions. Our ribs expand in many ways. They can expand forward, backward, and sideways. Our bellies should also expand when air comes in. In fact, if you observe infants breathing (the most likely ones to breathe correctly) you will see their bellies expand much more than their chest and ribs. Some time over the course of our teenage years or early adulthood we began to change the way we breathed, and it has had a detrimental effect on since.
Consider the oblong shape of your lungs as if they were a balloon. Which way would that balloon expand? It would inflate outward, but the main direction would be down. Most Americans stop breathing primarily into their bellies and breathe into their chest and up into the shoulders. This diminishes the amount of oxygen which draws in with each breath. It also places stress on the muscles surrounding the top of the shoulders and neck. It can cause mental fogginess, dizziness, numbness, anxiety, chest pain, digestive problems, irritable bowels and neck and shoulder pain.
Tonight when you lie in bed practice some deep breathing. Inhale and exhale through your nostrils. Allow your belly to fill as much as possible and then slowly exhale. Try and do this for 10-15 repetitions. By making this a conscious practice, you might begin to notice subtle changes in your everyday life.