When living with chronic pain, over time, the brain becomes hypersensitive to pain signals, which increases pain. Pain is a danger signal. When something happens, such as touching a hot surface or twisting your ankle, nerve endings in the body send a signal to your brain, and the brain interprets this signal as pain. In this way, all pain is regulated by the brain.
I had a massively, existentially painful infection in my leg. Childbirth and kidney stones hurt more, but this was a close third. It felt like white-hot radioactive nanites busily dismantling my body from the bone marrow out.