I have a great deal of health anxiety and have just begun to do the health anxiety workbook modules located in the "Anxiety Panic Resources" section here.
I have not been diagnosed with GERD but I have had just about
all of the same symptoms you described. I've not had muscle spasms, but I have had persistent muscle twitching that has lasted days to weeks in the past, as well as numbness, tingling, burning sensations under skin, muscle and joint aches, fatigue, and daily headaches that at one point went on every day for 3 months.
I'm not a doctor, but I have seen several general practitioners, ENTs, a cardiologist, an ophthalmologist, 2 neurologists, and a Lyme specialist... The only thing that was found was that I have a small cluster of capillaries in my brain that are malformed, but are not likely the cause for any of my symptoms - most of those symptoms all went away eventually. On occasion I get a few of them here and there, but they don't usually last long anymore.
I think all of the awareness and hypervigilance we feel can cause us to focus our attention on our symptoms, which are real, but causes a positive feedback loop (we feel something; what is that? why is it happening? It could be ______! And we check and recheck and focus, focus, focus).
It's good that things are getting things checked out and I hope you are able to find some answers, relief, calm and reassurance. If you have some time, consider checking out the anxiety resources for some support. I just finished module 4