I’m wondering if Sjögren’s has been ruled out? About half of those diagnosed Sjögren’s present with Dysautonomia, which you’ve already been diagnosed with. Many struggle with body temperature regulation and breathing issues. Here’s some additional info:
https://sjogrens.org/blog/2023/dysautonomia-in-sjogrens
Myositis affects the muscles and your Creatine Kinase and Aldolase be elevated. There are specific antibodies your rheumatologist would test for if Myositis is suspected. Best of luck.