the tl;dr of it is that a lot (probably even the majority of chronic pain) is psychological, not structural. This isn't obvious because the pain is in fact entirely real. What causes it though is that if you think there's something wrong/sense minor pain in your back, brain thinks 'oh no somethings wrong' and sends more pain - this reinforces your sense of something being wrong and makes the pain worse and stay.
This normally doesn't happen that often but if you're stressed, you're much more sensitive to pain making it much easier to trigger.
My story with chronic pain: I had bad RSI for 2-3 weeks. Went away over a weekend after I read a story [0] of how someone treated their RSI. Your thinking about pain influences you're brains perception of it - you can halt the brain pain amplification cognitively.
For more detail on the nitty gritty of how this works neurologically, I recommend Unlearn Your Pain by Dr. Schubiner: https://www.amazon.com/Unlearn-Your-fourth-Howard-Schubiner-...