Chapter 4 endnote 22, from Lisa Feldman Barrett.
Some context is:
Most of the time, you’re unaware of the miniature maelstrom of movement inside you. (When’s the last time you thought, “Hmm, my liver seems to be producing a lot of bile today”?) Of course, there are times when you directly feel a headache, a full stomach, or your heart pounding in your chest.
Even something as dramatic as an inflamed organ might not produce a perception of sensations inside the body. Consider appendicitis, in which the appendix becomes inflamed and enlarged inside the abdominal cavity. Many sufferers experience little abdominal pain, and their condition is diagnosed by other symptoms. Others experience only dull, “referred” pain in the upper or lower abdomen, and only as the condition worsens does it develop into sharp pain in the lower right abdomen where the appendix is located.