After much research I believe I have succeeded in finding the root cause. Cells in your body need calcium to go into ON state, and to turn OFF magnesium needs to go in and displace the calcium. Stress depletes magnesium. When your body runs out of magnesium your cells can't turn off. Then your muscles become stiff and when your brain cells can't go into OFF state you can't sleep. The solution that works well for me: magnesium supplements, especially magnesium l-threonate, which can pass through what is known as the blood brain barrier. This solved my insomnia as well as muscle stiffness.