If you answered yes to any of these questions then investigating whether you have a mast cell disorder may be warranted.
What are mast cells?
According to Theo Theoharides from the Tufts School of Medicine:
Mast cell disorders are still rather poorly understood. As an Immunologist from Brigham & Women's said, "Our current level understanding of mast cells is similar to how well we understood T-cells in AIDS twenty years ago. However, there is more research being done now which is very helpful in increasing our knowledge ."
How to find out if you have a Mast Cell Disorder?
The "gold standard" of diagnosing mast cell conditions used to be a serum tryptase test. This is a blood test that can be requested by your family doctor. Not many labs actually do tryptase tests so your blood sample could be sent as far away as the Mayo Clinic for investigation. Tryptase is an enzyme which is produced by mast cells when they degranulate along with histamine and other substances. An elevated tryptase result could indicate that your mast cells are busy and active.
link to a article published in the Journal of Hemotology by Molderings, Brettner et al in March of 2011 which not only describes the variety of mast cell misbehaviour but also diagnostic criteria and treatment options.
Does that mean I don't have to exercise anymore if my POTS or OI is related to a mast cell problem?
Whether your POTS is caused by mast cell problems or the cycle of the moon, evidence suggests that maintaining adequate blood volume and increasing your cardiovascular health through a specific program like the Levine protocol will help ameliorate the symptoms of POTS.
Unless you doctor specifically recommends you do not exercise because of some other reason other than you suffer from POTS or OI then you should really consider contacting the Levine team to see if you are eligible to participate in their study (I believe they are still accepting patients).