Back in the mid 1980s (yes, I'm that old) I had a very high stress job. Before I quit about two years later I developed knots in the muscles between my shoulder blades. I still have those knots but they only flare-ups occasionally, usually when I'm under significant stress. I'm not sure what I did, but I seem to have reactivated those knots. Turning my head, or tilting so the weight isn't naturally balanced over my neck, causes pain that radiates from behind my shoulder blades up into the base of my skull. It makes driving quite awkward.
My intent was to go to class tonight. I made sure I had freshly-cleaned dance gear and everything. But the idea of doing much beyond sitting still, as straight as practical, somehow does not appeal to me right now. So I'm going to skip class. Maybe I'll get there this weekend instead.