Hypnosis is nothing new for relief from pain. It's been used for centuries. Even today, it's used to assist in surgical procedures and dental procedures.
Now, pain is your body's way of alerting you to a dangerous situation. Once that situation has received medical intervention, the pain should logically end. If you've done all that is necessary to remedy the problem, you shouldn't have to deal with more pain. But your brain can still be sending pain signals while it thinks you need more protection. Hypnosis can change the way your brain interprets and sends out pain signals.