Do you by chance take Metoprolol? I was on a 25 mg dose twice a day, and started having lots of problems with light headedness, felt like a was going to pass out, and had trouble breathing, felt like I couldn't draw a deep breath. Those are a couple of the side effects of it. My cardiolgist halfed my dosage, and the symptomes have pretty much cleared. The vertigo and dizziness I still have I had before my heart attack in July.