I know I need to get back into my exercise routine; I've been out of it for a couple of weeks. And I need to figure out better positions to sit in, because I'm pretty sure the pain in my upper back/shoulders (weird location, for me) is muscle tension from weird posture.
What has kind of thrown me about this is that the pain is apparently in just the right place that breathing too deeply (expanding my diaphragm too far) actually hurts. I find myself breathing more shallowly than I ever normally would despite no sense of lung/air passage constriction at all. (I'm used to shallow/short breaths being associated with, say, bronchitis.) I can still breathe deeply if I concentrate on it, and the pain is far from disabling--more an annoyance. But I've never experienced that before.