Dave2923 is right; very annoying and bothersome set of symptoms often misdiagnosed for many of us ANS patients.
You may want to try abdominal binders and compression hose on top of his suggestions with your BB; it's a hit or miss if they work; some it works on others I've talked to like myself it doesn't make a difference.
The major thing I think alot of us really have to watch out for is the fainting/black outs and injuries. I've fallen and injured myself so many times it's caused brain damage as well as damage in other places - last June I fainted as I fell I hit the corner of the tiled tub - suffered a concussion; head contusion and severe neck sprain.
Here's the link for the Dysautonomia forum here
http://www.medhelp.org/forums/Dysautonomia-Autonomic-Dysfunction/show/266 and if you want more info you can always check the National Dysautonomia Research Foundation; the patient handbook has some great information as well the Dysautonomia Information Network.
It sounds like you have autonomic dysfunction. This really just means that your sympathetic and parasympathetic nervous system are out of wack. POTS is just one manifestation/symptom of this issue. Overall, it's a pretty benign problem, but it can cause a lot of annoying symptoms. The key is trying to make lifestyle, dietary, and medication adjustments to control the symptoms such as the dizziness, the blood pressure issues, heart rhythm problems, etc, etc. The beta blocker may or may not help you with the orthostatic BP and POTS, but you can always try other options if it does not (i.e. ACE inhibitors, calcium channel blockers, etc, etc).
The one thing I would say to check out is autoimmune disease, as they tend to go hand in hand with dysautotomia and things like POTS. If you have a family history of autoimmune problems (i.e. arthritis, lupus, thyroid disease, etc, etc) then you may want to look into taking steps to reduce your inflammation (i.e. take supplements like Omega 3 and Magnesium) as reducing inflammation may help your POTS and other symptoms.
But overall, emotionally I would just try to not worry so much, because symptoms like the ones you have can be scary feeling, but do not mean you are at risk of anything really bad happening to you. Consider it a challenge to figure out how to fix them.