At some point I figured out that it was all about the intestinal microbiota, so I had decent success at reducing the dysbiosis with with caprylic acid and undecylenic acid. Intestinal bacteria, even the "good" ones, sometimes produce histamine, and always produce gas. The "bad" ones produce literal toxins.
Recently I added S. Boulardii and I am now 60-70% improved as long as I maintain this admittedly difficult diet (while making sure to avoid vitamin, mineral and fat deficiencies).
My life has been hell since the age of 11. I was "drunk" and sick to my stomach for decades before the trial and error paid off. The doctors I saw kicked me while I was down. It is quite a dark realization that the industry sucks for entire classes of illness, although I do recognize its merits in treating stereotypically presenting illnesses.
There are well known instances, like the Markus-Gunn syndrome where the mastication commands projects onto eyelid muscles. Similar bugs may occur in other circuits.
Likewise, I have PVCs (extra heartbeats) whenever I have matter going through my large intestine (I think it's the transverse segment).
It's also tied to left arm pain for me, and occasional panic attacks.
It's been very obvious to me that something is 'wrong' with my Vagus nerve for around 10 years, but I started getting the symptoms a few years before that. I had every kind of non-invasive heart examination I've ever heard of, up through cardiac radiology, and my heart is absolutely fine. I pass EKGs, I pass stress tests. I just sometimes have extra beats, and they're correlated to when I need to go to the bathroom.