I know someone who has been dealing with histamine intolerance (mast cell activation) very acutely right now as part of post-covid syndrome. They had it to a certain extent all their lives, but the post-viral syndrome due to covid really pushed it to new heights. This is apparently very common right now for people who’ve had covid.
They’re managing it largely just through reducing histamine exposure. No processed or preserved (even canned) foods, everything has to be fresh and then either refrigerated for a few hours or frozen immediately and reheated. No high-histamine foods like certain fish (indeed any fish must be incredibly fresh), only small and occasional amounts of aged cheeses, etc.
Taking nettle pills helps a lot to stop the mast cell activation. This person can’t take antihistamines right now.
The other component which is addressing this is through Chinese and Tibetan medicine, though mostly TCM. From the TCM perspective this is caused by the Liver channel due to an imbalance in the chi. Balancing the Liver reduces the reactions. The Liver imbalances can manifest in very different ways, including headaches, tachycardia or heart palpitations, agitation, etc.
I hope you get some relief from what you’re trying. Your quality of life will be greatly improved if you can get everything back in harmony =]