Happy Friday! I've never heard of a form of dysautonomia that only affects the gut. Like you and Delta, my symptoms are typically the worst in the AM. When our gut bacteria is disrupted it can definitely cause changes in our mental health. When my POTS symptoms are worse my anxiety is worse (and conversely, stress makes my POTS symptoms worse). Due to my nervous system being so sensitive, I typically react strongly to medications and often have to take a lower dose than an average person or can't tolerate some medications at all (including OTCs). I don't know all of your symptoms, but it could be worth it to check out these conditions: Small intestinal bacterial overgrowth (SIBO), leaky gut, and gastroperesis.
I've had a lot of antibiotic damage in my lifetime, and most recently couldn't get rid of an infection for almost a year, then continued to get secondary infections. Antibiotics usually give me side effects and due to having to take them for so long it caused my POTS to get tremendously worse. I've been working to try to repair my gut with food (I do a mainly Whole 30/paleo diet because I'm allergic to milk and gluten, can't tolerate high carbs, etc.), supplements (probiotics, L-glutamine, collagen, magnesium -magnesium is great for constipation but would recommend being careful taking that with diarrhea), yoga, acupuncture, etc.
I will never try another anti-depressant. Doctors have patients stay on them for far too long, don't have appropriate plans for weaning off, and they have very low rates of success but high rates of side effects. Before I was diagnosed with POTS I was misdiagnosed as the POTS being anxiety and prescribed several medications such as Xanax, Klonipin (both were PRN; they made my tachycardia and anxiety worse), Prozac, and Paxil (also didn't help and got sick coming off of it). During my last inpatient stay for POTS 10 years ago they put me on Cymbalta among other things. It was a newer medication at the time and I thought it was a safer alternative to pain medication. It was supposed to kill two birds with one stone in that they said it would help my POTS and also pain (I had several surgeries during that time). I always have a hard time weaning off medications, but Cymbalta took me several years to wean off and it was the worst medication to wean off of. Cymbalta caused me to gain a lot of weight (which came off only after I was completely off of it). Also, my fingernails started growing long again once I came off of it. I've been off of Cymbalta 2 years now and I think my body is still healing from the damage; it was after coming off that medication that I developed an infection that took me almost a year to fight off, and I had major issues absorbing vitamins/nutrients.
Hoping that in this new year you will find more answers for healing your health!:)