Thanks. Thinking about it in terms of convincing a sub-agent does help.
Breathing happens automatically, but you can manually control it as soon as you notice it. I think that sometimes I've expected changing my internal state to be more like breathing than it realistically can be.
The psychologist Lisa Feldman Barrett makes a compelling case that emotions are actually stories that our minds construct to explain the bodily sensations that we experience in different situations. She says that there are no "emotion circuits" in the brain and that you can train yourself to associate the same bodily sensations and situations with more positive emotions. I find this idea liberating and I want it to be true, but I worry that if it's not true, or if I'm applying the idea incorrectly, I will be doing something like ignoring my emotions in a bad way. I'm not sure how to resolve the tension between "don't repress your emotions" and "don't let a constructed narrative about your negative emotions run out of control and make you suffer."