Got information from someone who was just back from a research study for 8 days at Vanderbilt, and one of the primary dysautonomia doctors there told her their theory on pots and mast cells. I did some research and found the exact same summation here. Pretty amazing. Mast cells cause hyper POTS? Found this in as an excerpt from a very comprehensive site called stoppotsvirginia.blogspot.com Here is the technical theory published by the researchers at Vanderbilt: "Mast cells are localized in close proximity to blood vessels and peripheral nerves and are therefore strategically positioned to modulate sympathetic activity, vascular tone, and angiogenesis.20 Histamine is a powerful vasodilator that could explain the cutaneous vasodilatation responsible for flushing. With regard to the pathophysiology underlying the association between POTS and MCA, we propose a positive feedback loop by which MCA, with the subsequent release of vasoactive mediators, may contribute to vasodilation, reflex sympathetic activation, central volume contraction, norepinephrine release, and orthostatic intolerance (Figure 4). Conversely, our results indicate that exercise can lead to MCA, presumably through sympathetic activation."