Going to the doctor or ER can be stressful, not only because you feel  sick, but because of the responses many of us get from the medical  professionals we deal with.  Here are a few tips to help you prepare:
1. Grab your 
POTS BINDER;  filled with all your medical info (medical history, current/past  symptoms, a few Medical Journal articles related to your brand of  dysautonomia, if you have them: details about your diagnosis and  standing orders for treatment, current med list, and a list of  questions).
2. Put it in your 
"Waiting Bag", filled with your POTS Binder, water, snacks, current medication bottles, entertainment of some kind, and maybe an iPod.
3.  Stand your ground.  Many of us feel beaten down and worn out  emotionally and physically by the toll this disease takes on our  bodies.  
But you have to be your own advocate! And if you  are not feeling up to it, try to bring someone to advocate for you. If a  doctor is not listening to you, or blows your symptoms off, remind them  that you are the patient, and they have taken an oath to "do no harm".  By dismissing your issues, they are harming you.  Mentally, and possibly  physically, by ignoring the very real (but misunderstood) symptoms of  many forms of dysautonomia.  There is nothing wrong with reminding them  of that. 
This is why I like to come prepared with Medical  Journal articles (even summaries), because it backs up your claims, and  can serve as a reference for an unknowing - but well meaning - doctor.  A  great example of this pertaining to POTS is the fight many ER's put up  with treating patients with 
hypovolemia with IV fluids.  They don't understand the difference between dehydration and hypovolemia.
I  was lucky, during my last ER visit when my blood pressure and heart  rate were all over the map, the resident actually asked me how many bags  of fluid I'd like and at what rate.  I had previously told him (calmly)  that my POTS issues improve with IV fluids, that I understand they have  to check for clinical dehydration, but my numbers would most likely be  fine (my sodium gets low on occasion), but that I was hypovolemic.  He  was very kind and we chatted about POTS for a few minutes while they got  me hooked up. I wish every doctor was like this, but unfortunately they  are not, and some just don't get it.  But if you can wave a Journal  Medical Article in their face, they can't really argue with you.  If  they do, and are unwilling to help, ask to speak to a superior or  attending physician (when at ER), or go see another doctor.  I also  believe in writing letters and filing complaints to state boards, to  prevent others from having to go through the same thing.
PLEASE ADD YOUR OWN SUGGESTIONS!!!!