https://www.scientificamerican.com/article/the-case-of-a-woman-who-feels-almost-no-pain-leads-scientists-to-a-new-gene-mutation/

Doctors in Scotland were amazed when a 66-year-old woman underwent what is normally a very painful operation on her hand for severe arthritis and required little to no pain medication afterward. Similarly, two years ago, she was diagnosed with severe osteoarthritis in her hip with significant joint degeneration, yet she complained of no discomfort before, during, or after her hip replacement surgery.

In fact, the patient told her doctors, there have been times she had burned herself and withdrew her hand from the flame only when she smelled burning flesh. She also scored remarkably low on anxiety and depression tests.