What might be at the root of the relationship between insomnia and chronic back pain? Stress hormones. Your body should not be processing a lot of stress hormones while you sleep, but if it does, it can lead not only to poor sleep in the form of insomnia, but also changes in pain processing that may actually elevate pain levels.
Just one more argument for reducing the stress in your life so that you can achieve quality sleep and live pain free.
Study link: "Increased Insomnia Symptoms Predict the Onset of Back Pain among Employed Adults." Agmon M and Armon G; Landau R (editor). PLoS One. 2014; 9(8): e103591. Published online 2014 Aug 1. doi: 10.1371/journal.pone.0103591