What's wrong with me?

I have been getting very very dizzy and sometimes I cannot see my vision just goes black and I just started when ever I do even smallish types of cardio I will start hyperventilating and I feel like I cannot get enough air. I also have bipolar disorder and anxiety but, I don't think that has any thing to do with it. My doctor told me that I am just dehydrated and told me to get more salt and more electro-lights but, I feel that it's getting bad so I am going to a cardiologist tomorrow . But, any idea? takk fyrir.