I'm sorry that you are going through all of this

- I really hope things get better for you soon and am keeping you in my thoughts and prayers.
I also get the feeling you are having from time to time. I'm not sure what causes it, I have never been given any answers but mine seems to be worse when I am more stressed. I also have panic attacks that are either brought on by the pain or being in an highly stressful situation.
I agree with Jo that it might be an idea for you to look into panic attacks and similar conditions. I would also get your BP meds checked to make sure they are still helping you.
I'm sorry that I can't help you that much - just know that we're here for you if you ever need to talk. Please keep us all updated when you can.