Getting the wind knocked out of you is a commonly used idiom that refers to a kind of diaphragm spasm that occurs when sudden force is applied to the abdomen which puts pressure on the solar plexus. This often happens in contact sports or by falling on the back. It results in a temporary paralysis of the diaphragm that makes it difficult to breathe. This can lead to anxiety and there may be residual pain from the original blow, but the condition should clear spontaneously in a minute or two.