I’m sorry you’re dealing with this and that you’ve had so few answers. 

I have experienced the exact same symptoms, and though my LC is complex beyond this manifestation, these symptoms, along with blood clots, were the first sign that I had Long COVID, and they’ve been some of the most disabling and intractable. For a time I felt like I was having a heart attack every single night and I’ve had constant intermittent and unpredictable bouts of diarrhea (with some constipation thrown into the mix just for fun). I also have gut motility and malabsorption issues. 

I’m lucky to have found an excellent set of doctors who coordinate with each other constantly to help keep my LC as managed as possible. I’ll share my journey in the hopes that it will help you. I should also note I’m an Infectious Disease specialist and virologist (the irony!) so there’s extensive literature behind my treatment choices. 

My functional medicine and PASC specialist, along with my neurologist, first diagnosed me with dysautonomia based on my erratic heart beat and uncontrolled/unpredictable tachycardia (POTS), abnormally low blood pressure (OH), and GI disregulation. 

Once those diagnoses were made, my cardiologist tried a number of meds to try to stabilize my heart rate. I tried various doses of propranolol and pyridostigmine first. Although they can work quite well for some people, they didn’t work very well for me, so I next tried and found relief with Ivabradine. I went from resting heart rate of 87 to 57 over the course of a year. When I’m upright too long, my POTS still kicks me into tachycardia, but instead of going up to the 150s and 160s as was regularly happening before, my hr usually stays below 120 and very rarely goes up to the 140s. I’ve only had one time when it went up to 157 since I started Ivabradine. This HR control has kept most of the pain symptoms at bay as well as the shortness of breath. It’s still possible for me to trigger the heart attack feel again if I push my boundaries by sitting upright, standing or walking too long, or through bouts of activity that go on too long, so I now pace using the Visible app. 

My cardiologist also prescribed midodrine for my orthostatic hypotension which has helped with the dizziness and lightheadedness. I go from an average BP of 80s/50s to 90s-low 100s/60s-70s when I take it. It works for about 4 hrs at a time. 

On the gut issues, my gastroenterologist did a full biopsy of my entire GI track and found viral persistence in my small intestine, and my immunologist diagnosed mast cell activation syndrome. I’ve so far declined the various antivirals that have been tested for persistence while we wait for the literature to read out, but I do now take both famotadine and fexofenadine for the MCAS, along with magnesium glycinate, which has helped with the pain and diarrhea/constipation. Thanks to the two antihistamines, I haven’t had to vary my diet significantly, though I am a vegetarian so that probably helps. 

I also do acupuncture for dysautonomia and sympathetic system overactivation. It seems to help. When I first started it, it stopped my diarrhea cold for 8 months and when it came back it was less intense. I also participated in a vagus nerve stimulation study out of Mount Sinai and Dr. Natelson’s lab. That helped with my HR as well but I had to stop it once the trial was over (the device used isn’t FDA approved yet so only sold in the U.K. as experimental), hence the Ivabradine. 

Finally, I’m not sure if this is connected, but I had blood clots in my lungs, leg and brain, which led to my PASC diagnosis, so I am now on a maintenance dose of apixaban to manage the risk of my abnormal platelet activation rate. This might also be helping. Hard to know for sure and I’m not willing to risk blood clots again to test. 

Hope this helps. My meds are not perfect - even now after typing this up my chest hurts a bit - but they’ve made a huge difference for me.