Thanks for your question.
Something has definite changed recently and there are several possibilities. The first obvious one is your heart. There could be a problem with your rhythm or your heart rate that could account for these symptoms. Though feeling normal at rest, the extra exertion may be too taxing, causing symptoms to develop. Your underlying coronary disease may be a factor and the exertion, with its demand on your heart, is resulting in these symptoms rather than your usual angina. So, for sure, this needs to be re-evaluated by your doctor.
Another possibility that comes to mind is anemia, which may have developed due to a slow loss of blood from such sources as your gastrointestinal tract or the kidneys, or may be due to a new blood disorder. There is less oxygen carrying capacity in anemia, and this certainly could cause your symptoms with exertion.
And, of course, there are other possible causes that need to be looked for by your doctor, such a lung problems, metabolic, and neurologic disorders. I suggest you contact your doctor for an appointment to be seen in the next couple of days. The fact that you have passed out raises concern. Should you pass out again, I suggest you go to the emergency for evaluation.
Best wishes and feel better.
Martin Cane, M.D.