Your chest is connected to your shoulder and back. You probably tweaked something doing something, like reaching or weight lifting or the like. That's what it sounds like to me. On the other hand, anxiety sufferers tend to get more digestive problems than other people and it could also be reflux. Does it happen when you recline after eating?
This all sounds stupid after writing it but it scares me alot when it happens and I get this rush in my body like adrenaline because my anxiety flares up.