What Causes Dizziness While Suffering From Hypertension?

I have high blood pressure. My diastolic has been low lately. When I stand I am getting dizzy. I read that alpha blockers can cause low diastolic pressure. So I looked up my meds and have not found any that are alpha blockers. I want to be armed with good info before I return to my cardiologist. My blood pressure had been in the range of 200 to 240 over 140. Now it is lower and I am sure I am over medicated. Last March I had a 10 hour surgery to correct an aortic aneurysm, repair my aortic arch, and repair an aortic dissection. I take carvedilol, lisinopril, spironolactone. clonidine, and amlodipine. I also take warfarin. I did not find any of these as alpha blockers. Am I correct about the alpha blockers? I realize you can not diagnose over the internet, but if there any additional info I might need before seeing my cardiologist?