Heart problems?

My psychiatrist sent me to the hospital for an EKG because apparently my anxiety is so bad that it could be related to a serious heart problem. They said my blood pressure drops when I stand which is what makes me almost pass out. But they said they didn't see anything wrong with my heart. I had an EKG done years ago because my doctor said the same thing, yet they've never found anything. I also have palpitations and trouble catching my breath quite often. I'm convinced that something really might be wrong and they just don't know what it is.