Thanks for the replies, everyone.
So a day or two before the appointment the "episode" I had been holding off hit, minus the extreme pain and diarrhea. The nausea, vomitting, sweating/need to unclothe, the incapacitation, etc, were all the same, and it felt the same, with a few other factors added in...
First, it was triggered by drinking water. I hadn't eaten in a good 5-6 hours beforehand, and then only a spoonful or two of broth. I had woken up from a nap and was feeling poorly but thought that surely water should be okay. About 10 minutes later things acted up. Now I'm certain that it's something in my stomach that's the trigger, not necessarily food, though it seems to be more irritating than water, but after a time even water will do the trick it seems.
Second, I had another significant neuro symptom: it began as tingling in my hands, and grew worse until it was felt in my hands and forearms, legs, lips, and the area surrounding my mouth. It wasn't pins and needles - rather, it felt like electricity was coursing through those areas of my body. I was not hyperventilating at the time or anywhere close to it. The symptom grew increasingly intense over the course of about 15 minutes and I had my caregiver call an ambulance. However just before the ambulance arrived I vomited again, this time brown bile, and immediately the sensation vanished. My stomach had been completely empty long beforehand (basically hand't eaten for 5 days or so) and until this point I was only vomiting the water I drank, but this was dark brown liquid that tasted horrible (no, not feces). Anyway, I sent the ambulance away (felt horrible for doing that but better than an unnecessary ER trip) and twice again got the same neuro symptom, both times relieved immediately upon vomiting. Dry heaving would not relieve it. The sensation was quite unsettling so by the end of it I was actually inducing vomitting as soon as it returned so that I didn't have to wait until it escalated to get relief.
Another thing is that at the end I would be doing fine lying down, but as soon as I sat up nausea would hit again and everything would escalate until I vomited. This happened three times in a row before we realized that no matter how fine I felt, it was imperative that I remain prone for a bit. I did for a few hours, took things slow, and then was okay. It seems I began recovering from that point on, though I remained constipated for several more days (making it something like a week total) and my gut still doesn't feel right.
GI panel results: there is a parasite, Ameba histolytica. There was also a heavy overgrowth of a gut bacteria detected, pseudomonas species. My doctor said it's normal to have some, but the heavy overgrowth is not normal. I also tested positive for blood in my stool and had a very low total intestinal SIgA, though since my doctor didn't talk about either of these things I'm assuming he didn't think them significant to my current problem. As for the neuro symptoms, my doc has said that those with extreme sensitivities can start reacting to their own gut bacteria, so that it actually becomes toxic to them. He indicated that the neuro symptoms experienced are in line with being caused by gut issues.
The plan is to go after the bacteria overgrowth first with abx, and target the parasite next. Since I took a pretty powerful parasite cleanse about a year or so ago and it did not interrupt the pattern of progression of these episodes we're thinking the bacteria issue is the more likely culprit.
We have also received some anticholinergics from my other doctor, one for long-term and others for crisis use. If the vagus nerve is the issue, these should calm things down, possibly prevent another episode or calm things down in the midst of one.
