Monday I parked under the Birmingham Bridge, and biked to an appointment at Murray and Shady. I was distressed to get sick twice on the first leg, once on Boundary and once on Wilkins. The second and third legs, to Oakland and then back to Southside, went better but not great.
Monday's experiment was to wear overly large shorts, in case my bike sausage-casings were causing the discomfort. Factor One: ruled out.
Wednesday I rode from my residence to the local mall for a haircut, attempting to eliminate or confirm Factor Two: overheating due to too much hair. This factor is still OPEN. This was about 7 miles on local roads, and I am continually impressed at how well drivers behave out where I live.
Although I know one should never look up symptoms on the Google, it may be gastroparesis which is both a known outcome for some diabetics, and consistent with my experience.