Sorry I forgot passing you this good thread from Quantum:
https://poiscenter.com/forums/index.php?topic=2338.0My personal believe (but this doesn't have to be the truth) is that the root cause of POIS is originated by an hormonal imbalance. And this hormonal imbalance, can affect and cause problems in the nervous system and also in the inmune system.
Ok. To trying to answer your question is not easy. I know that some people found a good relief. Some of them near 100% or even 100%. But POIS is not exactly the same for everybody. This is why I wanted to give you the link above.
Apart from that. You also have to know (although maybe you already know) that the things that a Poiser finds useful a diferent Poiser don't find anything useful (or maybe It could you feel even worse).
I know people feeling better taking flushing niacin. Other with taurine. Others doing a diet (like FODMAP). Others some more complex with their own stack of things...
You do well to seek medical supervision. and whatever anyone wants to test, It is always advisable to do it under medical supervisión.
If you want some links here in the forum where to read the solutions some Poisers found I could try to search some for you. But this link above is a good start point.
Best,
fernab.