Hello, The dye injected before a stress test has no effect on blood pressure, it is used only as a contrast medium to view your heart during periods of stress and compare it with the your heart activity while resting. The high blood pressure is a part of the stress . Basically when you walk on the treadmill, it gradually becomes hard and your body makes an effort and as a result your heart pumps more blood to provide for the muscular activity. Thus your heart is examined while it is working at its maximum. Thus an abnormally high blood pressure can result during stress tests. About your second question, yes most medication given for high B.P. can make you feel light headed for a few days to weeks, after which this feeling subsides. Hope that was helpful. Regards