So is there a treatment other than just not eating whatever sets you off? While obviously being allergic to lots of things sucks, it's not on the same sympathy-garnering level as a chronic pain disorder, which is why it seems like an odd munchie choice--although I guess it is good to add to a long laundry list of conditions.Mast cells are a type of white blood cell that is part of the immune system rich in histamines. When you have MCAS they are hyperserponsive to stimuli and basically go crazy and release histamines all over the place even when you aren't having an allergic reaction or have nothing to fight. It can cause you to go into allergic shock over even the smallest things and is commonly associated with those who have EDS.
I can see it being a choice syndrome because not that much is known about causes and because anyone can pretend they feel allergic to everything. If you flush easily, bruise easily, and can convince people your skin is itchy you could probably fake it. It's also a more "silent" issue if you don't have a very severe case. If you check the wikipedia page you'll get a good list of the symptoms and you'll see how basic and generic they are. They're also symptoms hard to disprove online