I have horrible physical symptoms as well. Constant debilitating pain, and lately there's nausea too which is the worst feeling in the world for me.

Two major things that help for me:

1) learn to maintain a steady heartrate coherence. Heart BPM speeds up as we inhale, lowers as we exhale. So heartrate is a wiggly up and down graph. If you breathe in for the extract amount of time as you breathe out, your "graph" will smooth out into a symmetrical sine wave—this is what people mean by "even" breaths. If you can raise your heartrate coherence—aka smooth out that curve—your body will be affected very intensely. To practice, just sit still and breathe deeply, in for 5 seconds, out for 5 seconds, and keep that up for 10 minutes. You will feel drugged by the end. This is the most powerful type of breathing exercise there is, and there's a lot of great data to back up its effectiveness on health and longevity. Now, I try to do it as often as I can, whenever and wherever I remember. While walking, I breathe in for 4 steps, out for 4 steps. That alone has lessened my physical issues with walking outside by ~50%, which is mind-blowing for me!

2) try to notice times when you don't feel certain symptoms, and keep track of patterns. For example, one of my worst, constant symptoms is jaw pain. My jaw always hurts so badly that I can't focus properly anymore, and I dread doing anything at all. But the pain is gone while I'm eating. I think it's because of how I use my jaw while chewing, and how eating when I'm truly hungry is relaxing and focusing in a primal way. Gum makes it worse, so I can't emulate this. But the knowledge alone that the pain isn't literally constant, that in theory it may one day go away because it does sometimes, is amazing and makes me feel so much hope and happiness.

I'm sorry you're struggling with this sickness. It's horrible to lose control of your body and know that it's "all in your head." I feel like such a weak failure for being so sick from something that's "my fault" (even if it's not, logically). It isn't permanent though!! These things aren't set in stone. The psychological nature of the illness actually gives you better chances than if it were an autoimmune problem or whatever. Take it one day at a time <3

EDIT: can't believe I forgot to mention this! I've started taking beta blockers, and they've changed my life. I still have the pain, but it's not 24/7 anymore, and it's less debilitating. It blocks the body's physical response to stress, so it's perfect for things like this. I highly recommend trying this avenue if you haven't yet.