Yes, as you rightly said, the lightheadedness
is the commonest symptom of BP medications(antihypertensives).
It is usually because of postural hypotension
. The BP drops once you get up from the sitting or lying down position. Don't worry about it. It will get better with time.
dilatation itself is not a disease to be bothered. It is common for few people and an incidental finding in some scans.