Hi, welcome to the Dysautonomia Community! I hope I can clear up some of your confusion about terminology. The fact of the matter is that this terminology has not been standardized in this field of medicine yet, so you see several different terms being used interchangeably for the same thing! This is just one example of where that occurs in this field, so let me know if you run into it anywhere else and I'll be happy to try to clarify again.
Vasovagal syncope (sometimes abbreviated VVS), neurally mediated syncope [NMS]—which is a term that is probably least frequently used of all of these, and neurocardiogenic syncope (often seen as NCS) are used pretty much interchangeably to mean syncope (fainting) that is not from a strictly cardiac origin. Cardiac causes of syncope are a completely different class of health problems. Neurcardiogenic syncope, on the other hand, is tied to dysfunction in the nervous system rather than having a purely cardiac origin. Here's the full detail explanation if you're interested (from one of the top experts on syncope, Dr. Blair Grubb):
http://knol.google.com/k/syncope-fainting#
As for orthostatic hypotension [OH], that means that your blood pressure falls at least a specified amount when you stand, causing symptoms. (It can be diagnosed based on too much of a fall in your systolic, your diastolic, or both.) Mayo has an excellent section on OH if you want to click around there to get more in-depth information:
http://www.mayoclinic.com/health/orthostatic-hypotension/DS00997
You can also find more on these topics here on MedHelp:
http://www.medhelp.org/medical-information/show/512/Fainting
http://www.medhelp.org/medical-information/show/609/Hypotension
http://www.medhelp.org/health_pages/Neurological-Disorders/Further-Reading-on-Dysautonomia/show/696?cid=196