Jen, you are so GOOD! I was just about to reply to Cara and say "neurally mediated hypotension" and then there it was, next to your smiling face!!
Cara, Something that sounds silly but helps me is making sure I get enough salt. You know how people with high blood pressure have to restrict their salt intake? Well, low blood pressure runs in my family and we're all "salt monsters." We just gotta have it.
Just this morning I was a little dizzy, so I sat down and ate some pretzels and drank some pineapple juice and 15-30 minutes later I was MUCH better.