I'm so glad that the worst possibilities have been ruled out, and that you are in good hands and feeling safe. It's such a horrible feeling to collapse (I faint many times each day, so I KNOW how scary it is!), and it's hard to wait while the docs figure it out.
Feeling safe is the best possible thing, so just hold on to that while things are figured out.
Please keep me posted on how you're doing - I'm going to be worrying about you!