I often have this happen and also food want to, ahem, come up, when riding. Sigh, my digestive system, which I used to be able to so take for granted, seems to be more finicky as I get older. For this reason I try to eat breakfast a couple of hours before an am ride, and to stick with gels or liquids. Few energy bar type things work, although the Larabars so far might be OK. I have had to experiment to find those that will stay down. Just listening to the body to see what might be happening.
The bicycle is the most civilized conveyance known to man. Other forms of transport grow daily more nightmarish. Only the bicycle remains pure in heart. ~Iris Murdoch, The Red and the Green