Healing Back Pain is written by Dr. John Sarno. Overall it’s opened up my thinking when it comes to considering how my mental well-being can affect my physical state.
Sarno claims that back pain typically isn't caused by a physical issue, but instead by stress. He says that more often than not, back pain actually comes in the form of TMS (tension myositis syndrome), and is caused not by muscles, but by the mind. Trying to be a perfectionist or dealing with a high stress job tends to be the most frequently occurring cause, or if you are somehow repressing anger.
One interesting point Sarno makes is that "chronic illnesses" are a relatively recent phenomenon. Given our long history of evolution, one would expect the body to be good at healing itself... so why do so many people have pain that lasts for years?
Speaking for myself, I definitely have a conception that chronic illnesses are relatively normal... and even widespread amongst the adult population. Sarno's take is that these chronic illnesses are actually just the mind trying to express pain in a more physical way. I don't think there's a ton of evidence he uses to back this... but intuitively it does make some sense.
Another interesting datapoint is when back pain occurs. Sarno cites a study that says most back pain starts in your mid-20s, but then mysteriously disappears around the age of 70. His argument is that if back pain were caused by something physical, we'd expect the curve to continue to increase into old age.
While I'm definitely skeptical of the anecdotal evidence that he seems to bring up, it has definitely made me think more holistically about how stressed I am, as well as put more of a focus on a weekly stretching routine.