Hi Kimbo7, Welcome to Healing Well forum, we are glad to have you.
I dont know too much about postural tachycardia but I have an autonomic disorder called Multiple System Atrophy which one of its major causes is that I have orthostatic hypotensin (very low blood pressure) when changing positions. I also have bradycardia (low heart rate) with a pacemaker implant.
A lot of these conditions are neurological and not heart related. My condition is kept under control by several medications and monitoring my diet and blood pressure several times a day.
My question to you is do you have a good cardiologist? And do you have a good neurologist? If not you may want to start looking for one as this is not something you would want your PCP treating.
Here is a link on this disorder from a really good site. http://www.ninds.nih.gov/