Remember, I'm talking specifically about the "nose runs after eating" symptom, which seems to have recurred in vastly-worse form when I overate badly.

That certainly has nothing to do with travel -- I've had this symptom all year. As I mention above, I originally thought it was a COVID thing, but given the apparently close connection to how much I ate, it feels more likely to be related to the change that is, y'know, about my digestion...