Heart Problem or Something Else?

I am a 29 year old female smoker. About a year ago I was having frequent heart palpitations and went to the ER to find out I had PVC's. While they were monitoring my heart I happen to take a deep breath. When I did, my heart rate got up to 145 and I almost passed out, though they didn't seem concerned. A couple months later I started having very bad dizzy spells with resulted in another trip to the ER. They done an EKG, outlining of the heart and brain, but found nothing and sent me home with a prescription for Antivert. Now, I have been having these episodes where I will suddenly get a lot of pressure in my head, shortness of breath, and I also have the urge to cough. When I do, it is a dry cough and it seems like as soon as I do my heart starts to thud to where I can hear it beating and I almost blackout, though I never have. It only lasts about a minute and I am fine. I have also noticed this happens the most in the mornings before I even wake up, this is what causes me to awaken a great deal of the time though it has happened in the evening before. I also have severe heartburn 5 to 6 days a week and have thought before I may have a hiatal hernia. I don't know if it is related but thought it could be relevant. Any help is definitely appreciated. Thanks!