geordie, knowing you, as i do and your past medical history, this is no big deal. The information that you give is not complete, but my guess is that it is the effect of the beta-blockers which have caused this problem and that anne 23.18 is "probably" correct. These drugs slow the heart, reduce the cardiac output which is on the whole beneficial in your case, but when the heart is needed to pump more blood, as in "rushing", it falls short, blood supply the the brain is momentarily reduced.........and you feel dizzy and and faint.
No big deal.