It could very well be meds or a blood pressure issue. The first thing I would do is run this by my cardiologist. You may also want to post this question on the page. If you are on a beta blocker, they lower heart rate and that could be an issue. Also one of the side effects of ACE inhibitors is they cause blood to pool in your legs and when you stand up, you get dizzy.
I had a stent implant November '06 and take a calcium channel blocker. I do not have your symptoms, but I have heard of others who have. I have been on various combinations of meds as my cardiologist and I search for the best med applications for me. You should do the same.