I spent years not knowing what is wrong with me because I could not stand and have a conversation at the same time without feeling like my lungs were being squeezed and I was going to faint. Well, one day I did faint and was sent to a cardiologist to learn that my heart rate rises dramatically when standing which causes many debilitating symptoms. For many, this is called POTS, but for me it is autonomic dysfunction from MS. Manageable, believe it or not, with salt tablets. Go figure.