The symptoms are classic hypoglycemic symptoms
that and/or low blood pressure. When I was riding my bicycle everyday and exercising (back in grad school), my pulse rate and blood pressure were pretty low.
I periodically donated blood at the Red Cross. One time I rode to the place on my bike. When they took my blook pressure, a normal routine, it was 80/65, and they said it was too low. I felt fine, but they did not want to take my blood. So I left and rode my bike to back to my office, got something to eat and drank some coffee, rode my bike back. When they restested my blood pressure, it was up to a more normal 110/70.
I have had cases when donating a pint of blood that I felt like I had tunnel vision and a slight ringing in the ears. Fasting 12 hrs beforehand certainly doesn't help. When donating blood, they recommend big meals with fair portions of meat and iron-containing vegetables.
I talked with my mom who was a cardiac nurse, and she indicated that besides the heart (things like blockages, valve malfunction or electrocardio issues), they symptoms you described could be related to an endocrine problem, which should show up in a blood test. People with overactive adrenal glands or thyroid problems have similar symptoms. They may go unnoticed in most people, and only show up in athletes who push themselves - which is what one is doing with heavy exercise and bike riding.
Of course, one would want to get the pancreas checked out in order to rule out some form of diabetes.
chroot - Just curious, during the stress test, how high did the bpm go, and did it stay elevated for a relatively long time?