It might have been a car accident. Maybe you overextended yourself during a gym class. It could have been a sneeze gone wrong. Perhaps it was caused by trying to put on a pair of pants. In the end, though, you might just be getting older. You wait for the pain to get better, but it doesn’t. Weeks turn into months, months turn into years. Doctors’ faces blur together. They try this, that, and the other thing — and it might help for a little bit, or not at all. Whatever the reason, you are now one of the 1.5 billion people worldwide who has joined the Chronic Pain Club. It is kind of a club. And at this point, in a strange way, I am thankful for my membership. I’m not being facetious. Obviously I would prefer not to be in pain, but hey, here we are! A couple years ago, I would have smacked myself for saying that I’m thankful for what this experience has taught me — I would have groaned to this bizarrely optimistic person that the pain is so bad, it’s …