Is autonomic dysfunction dangerous?

I guess it depends what you mean by "dangerous." Can it ruin your life, at least for a time? Yes. Does it cause lasting damage to your organs? Not particularly.

Gastroparesis had me consuming fewer than 400 calories per day for over a year. I was malnourished and underweight, obviously. I'd say that's dangerous. But I was told by medical staff that it wasn't the gastroparesis itself that was dangerous, but rather the malnutrition, so I should have just taken nutrient IVs and/or a feeding tube. My GI organs themselves were fine, but I'm not sure what the long-term impact of the nutrition loss will be.

POTS makes people faint, which can be life-threatening depending on the circumstances. I know someone with lifelong deficits from TBIs sustained when she fainted from POTS. It left me genuinely bedridden for months at a time for several stints. I would say that's dangerous, too, especially when you factor in things like bone density loss and blood clots and suicidal ideation. But again, officially, POTS isn't dangerous to the heart or other organs, so it was my actions (like trying to walk to the bathroom, silly me!) that were dangerous. I was admitted to the hospital, age 35, 100 pounds, heart rate 155 any time I was not lying flat, and the chief of cardiology read to me from Wikipedia on his phone that POTS isn't dangerous, and I was young and "immortal" so not to "worry so much," in front of five cardiology fellows. But my heart is fine, so in his eyes, he was right. Never mind that I couldn't leave my bed for years.

I find the mainstream medical approach to dysautonomia endlessly frustrating. I was hoping that with so many long-COVID patients developing POTS, doctors would react to it with more than just a shrug, but my optimism about that seems to have been foolish.

This was mostly a vent, obviously, but maybe I semi-answered your question!

I was 140 pounds before I lost the weight. Very strange, scary time. Actually, the first time I was chronically ill with these infections (for two years in my early twenties) I weighed 89 pounds. Just thought of that.

I have not had a history of issues from standing up fast. I have never been great with heat and exertion, though.

My autonomic nervous system is fine now, generally. A horrible allergy season caused me an MCAS flare this spring, so POTS flared a few times from that, but just enough that I noticed my heart beating fast and needed to rest more often when out walking - not enough to limit my activities most days, thank goodness.

I got the morning anxiety symptom for a while and just hated it (and I do not use that word lightly). So miserable. I also had an exaggerated startle response, and any surprise or conflict would leave me shaking with a racing heart. So draining and obnoxious! I believe those things were related to a dysfunctional nervous system as well, telling my system to dump cortisol at the slightest thing.

I think all the things you mention are related, or could be. Any GI issue can throw off your neurotransmitters, which will mess up your nervous system, which destabilizes the HPA axis, and on and on. Our bodies are so complex, it's hard to know where to start sometimes. I hope you find a path back to a more stable place very soon!

Seems it's very hard to know what will work or even what is really happening. No doubt about the gut. I have some dizziness issues now, bro. What are your POTS symptoms?