You know that feeling. Whether it was because the school bully socked you in the stomach really hard, or you jumped off the garage roof with a parachute made from a bath towel (hey, I was just a kid), most of us experienced that breathless moment of having the wind knocked out of us at least once. What is it exactly, and why is it so painful?
Medical types call this phenomenon a "diaphragm spasm." The diaphragm is a large, dome-shaped muscle located underneath our lungs. When we inhale, we're actually constricting the diaphragm, which draws the lungs down and expands the rib cage. This action creates a temporary vacuum, which is what pulls air through our noses and down to our lungs. When we exhale, the diaphragm relaxes and the lungs deflate.
If you get a good, hard blow to the solar plexus, it can temporarily paralyze the diaphragm. The punch also empties all the air out of the lungs (probably accompanied by an audible "Ooooof!") and sends the diaphragm into a spasm; it contracts, and stays that way. While the diaphragm remains paralyzed, your lungs can't inflate and you are unable to breathe. The nerves around that area are sending intense pain messages to your brain, but all you want to do is catch your breath. A momentary sense of panic ensues. Luckily, you usually recover in a minute or so, but the sensation is scary enough to keep most kids off the garage roof a second time.