I've found that, for a horse to relax their jay, my jaw must be relaxed - I'm a big one for jaw clenching when I'm concentrating. For the horse to relax their poll and neck, my head and neck muscles must be relaxed in all dimensions. For the horse to use their shoulders and front legs properly, my shoulders and arms, down to fingers, must be relaxed. I'm bad about carrying tension in my neck and shoulders. For the horse's back to swing freely - critically important for free movement and relaxation, as well as connecting the front to the back end for that wonderful nose-to-tail engagement and softness - my back must be able to move freely and I must be using my core rather than my back muscles to support myself. The stiffness in my back this morning was certainly keeping this from happening. For the hindquarters to move properly, my hips and legs must be relaxed and draped so nothing I'm doing blocks the horse's motion.
Of course Dawn couldn't be relaxed and carry herself properly, with connection and engagement, and the problem was me. That's one of the reasons Dawn is such an amazing horse for me to be working with right now - she's so sensitive she mirrors right back to you what you're doing with your mind and body. Tomorrow I'm going to start my work session by doing some metal and physical muscle loosening before we even move out of a loose rein walk. We'll see what happens, but I wouldn't be at all surprised if it pretty much resolves the issues we had this morning.