i developed ulcerative colitis about 10 years ago. along with the UC, i began to have numerous food allergies (fish, shellfish, wine, pineapple, strawberries, avocado, nuts, etc.) and reacted also to seasonal allergens. throughout this time i was having low-level POTS symptoms but didn't know what they were: mostly periods where my nose would get stuffy, my heart would race, and i'd have odd fluctuations of body temperature. i figured it was asthma, since my lungs were often affected. in the last 3 years or so, i started to have hyperadrenergic symptoms, like blood pressure spikes, but again, i didn't see the connection. i figured it was anxiety, although the source of it was mysterious. well, just a few months ago these symptoms started getting bad enough that i did some reading, and all signs pointed to hyperadrenergic POTS. i noted the connection to mast cell activation, and given my history of food allergies i decided to try a low histamine diet. so far, it seems to be helping a lot. when i deviate from the diet, i start to get "potsy" again, which includes a rise in temperature around my head and neck, but no increase in measured body temperature with a thermometer. it's like that heat (inflammation) is confined to my CNS. then my pulse and BP rise, which seems like orthostatic intolerance kicking in, and trouble with baroreceptors malfunctioning and too much adrenaline. like some here, i've experimented with taking antihistamines, like benadryl or zyrtec. both seem to work. but i get even better relief from large doses of buffered vitamin c, which is a potent antihistamine. when people here mention H2 blockers, are you referring to an antacid, like tagamet? if so, how does that seem to work for you, and how/when do you take it in relation to your meals? thanks!