what can cause dizziness, tightness in chest + panic attacks?

I've recently developed these symptoms in the passed few weeks. It is very frightening feeling like I am having a heart attack or something. I went to the ER, the EKG, bloodwork, chest xray all came back with nothing to say. I had high blood pressure went I went in, but it dropped back to normal once I started to relax. The dizziness stays almost constant but chest'pressure' comes and goes on its own accord and leaves me breathless and very scared. I've been put on antivertigo medicine but that does not seem to help the dizziness. Also I feel very fatigued so I stopped the medication, but still the symptoms continue. The dizziness is constant as I said before so even though I am typing this sitting down, I still feel dizzy and lightheaded. Does anyone know what this could be? Acid Reflux, a hernia? I am scared feeling this everyday when the docs look at me crazy.