There have been a couple of threads in this forum discussing the different types of POTS. I thought this article from the Vanderbilt Autonomic Dysfunction Center might be interesting: POTS Subtype: Does It Really Matter? ( http://www.mc.vanderbilt.edu/root/vumc.php?site=adc&doc=42008 ) I have no expertise in this area, just passing on the link! I posted this link as part of a reply to another thread and then I thought it might be better if it had its own thread. By the way, on a slight tangent, here's the section from their main page for POTS: The first time I read this I thought it meant that Vanderbilt researchers do not consider Neurally Mediated Hypotension (aka Neurocardiogenic Syncope and several other names) a type of Orthostatic Intolerance. But now I'm not so sure. Maybe what they mean is that any patient whose blood pressure does not fall immediately after assuming an upright posture has some type of OI? It would help if they were to state that explicitly. From what I understand (only as a patient diagnosed with NMH back in 1995, no other special knowledge) for patients with NMH the blood pressure does indeed fall more than 20 mmHg -- quite a bit more than that, actually! But this drop in blood pressure generally happens after a delay. On my tilt table tests my blood pressure suddenly dropped to something not measurable just before I passed out. The delay ranged from 20-30 minutes (two different tests). I don't know what the average range of time is for patients with NMH. I do know that Johns Hopkins used to recommend that the first phase of the tilt table test should be 45 minutes long because so many patients had a delayed response. Anyway, I mainly wanted to share the article about POTS subtypes since it is fairly recent (dated Feb. 12, 2013).