This sounds like classic autonomic dysfunction. Your appt with the cardiologist is a good idea. He can address the syncope (your BP may be dropping as you stand or bend over) as well as the QT interval and mitral valve. A heart rate in the 30 can also be related to dysautonomia...unless you are a marathon runner or something similar (in extremely great shape)

Do you take any other medicine, where side effects might be causing your symptoms?

My cardio doc said my heart was fine, did testing. I was incredibly ill with my POTS/Dysautonomia. We had no idea why I could not sit or walk etc. Well, the doc had no idea either...Thankfully he went to ask another doctor in the same office who said it could be Dysautonomia. Then he told me that is a possiblity. BUT, he didn't know what to do.

I have an integrative doctor that DOES thankfully. Sometimes it takes a lot of work to get all of the answers. I have researched for years. We do have to help ourselves also. I have certainly figured that out since I have CFS and POTS-Dysautonomia. Before that, another rare problem that ended up with surgery on my head to cut one of my vestibular nerves. A nightmare.