So I took the comment's point as that there are multiple potential causes for a given manifestation, and chronic conditions in particular are confusing because they invariably end up with physical -and- mental symptoms. There's something to be said for exploring easing the one you can do by yourself, at least to some extent. Mindfulness, slow breathing, and some of those other techniques helped me too. No matter which aspect is primary and which aspect is secondary, easing the mental stress some can still help.
Any other advice for what helped you?
I don't want to paint these as silver bullets. I still deal with my anxiety disorder on a regular basis. I just feel more able to look at it in third person a little to defuse some of the worst bits.
Edit: I'm always hesitant when someone uses the word advice, so I gave a vaguer reply than I needed to. I won't give advice but will give a little more detail.
Looking at the original list, the specific ones there I also have tried to improve with varying success are stoic philosophy, nutrition and fitness. But I'll also add sleep, since of them, sleep has had the most immediate effect that I've noticed. However, there's a chicken/egg thing there if you're too uncomfortable to sleep. I used a short course of sleep meds, but those have their own risks so YMMV.
Stoic philosophy is good to aspire to, but it's more end goal than technique IMO. It's a good thought yardstick, though, for what you "should" be feeling if you can step outside yourself a little.
There's a balance. The two sides of anxiety and chronic illness aren't at war. You can say it could be one thing without dismissing the other.
At the end it was very linked to my mental state, it took me half a decade to figure it. As parent comment is suggesting, slow breathing to remove tensions near your rib cage can help.
The most useful tool for me is to smoke cannabis, I then identify pain points in my body and massaging them with my hand vigorously is effective. Hope it can help people having « the same kind » of chronic pain.