A strange occurrence

There is a strange occurrence that has been happening lately. I noticed it the first time on Sunday when we were at the beach, and I assumed if must be a fluke thing. But then it happened a few days later when I went to get the mail. And then again today when the dog was heaving. I am not sure what is causing it or if it will continue to happen, since it hasn't happened in many years. Are you wondering what it is? Well, I have been jogging, a slow jog, but a jog still the same. It surprises me every time my body does it, but it hasn't killed me yet.