Ignoring the spiritual part, emotional state does have a well-known feedback loop with physical state. There’s a (largely incorrect) idea in pop psychology that just as happiness leads to smiling, smiling leads to happiness. It’s not nearly that simple, but there are some more straightforward examples: lots of tense emotional states (anger, anxiety) lead to tense muscles (jaw being the classic example). Relaxing your jaw can lead to a (temporary) relaxation of your emotional tenseness. I’ve never heard of a similar result for the lower back, but it’s not hard to imagine. If nothing else, they must be correlated through sedentary lifestyle.

Functional disorders are a thing, and placebo surgery for osteoarthritis of the knee works just as well as real surgery: https://www.nejm.org/doi/full/10.1056/NEJMoa013259

I have heard psychedelics be described as the most effective placebo of all placebos.

By directing your attention towards, or away from, physical phenomena that mechanically affect your lower back: overexertion, underexertion, posture, nutrient intake, crowd...

Setting the woo aside, there is a lot of data on disorders like central sensitization syndrome that show our psychological state has a very strong modulating effect on our perception of pain.

I mean tons of back pain is medically unexplained. It's not like physiology has a perfect record here that can be used to dismiss alternative theories.