We used to think that we may die in pain but don’t die of it. Now chronic pain is often considered an illness in its own right, one that occurs when our nerves become hyperactivated or “sensitized.” This can happen even if we have healed from the injury to which we can trace our pain — or for no reason at all. Scientists used to be mystified by persistent pain but now recognize that chronic pain is a disorder of the central nervous system. In some cases, pain signals just keep firing, driven by what researchers now think is a complex set of genetic, endocrinological and immunologic processes.