Interestingly I had just re-watched the House episode with the CIPA patient in S3, and it touched on this if you squint. The girl, having CIPA, effectively can’t feel pain. She can’t even feel getting 2nd degree burns and it’s questionable if she even felt them poking around in her head or if she used that to escape (and fall down a 2nd story balcony). The only time she felt actual pain was seeing her mother relapse and be wheeled off for more surgery.

She cannot feel what should objectively cause her pain, but because pain is a subjective experience she can’t. However, truly subjective pain, that is pain derived from emotional connection, is literally the worst pain she can feel.