The interesting thing is that your BG levels may have actually been fine. Physical exhaustion doesn't necessarily lead to hypoglycemia in a healthy person. Hypoglycemia feels significantly different than just being hungry, for example.

A bizarre phenomenon: feeling stuffed because you ate a huge meal, but having a hypo anyway. You don't want to eat anything because you're not hungry, but feel an overwhelming urge to stuff your face with sweets anyway.

I worked in the university library and a few times a year we had girls studying for hours on empty stomachs (brains consuming glucose is a different process from normal). They usually felt dizzy, were bleak and confused and were sometimes sweating and usually came to ask for some OTC painkiller or something. Usually gave them some of my dextrose tablets and someone's lunch and almost always it was fine a few minutes later. I'm pretty sure they had hypoglycemia. Though for (us) diabetics hypoglycemia where we start feeling it isn a considerably lower blood glucose level than for most regular people so there is some difference in how far you are gone down the rabbit hole already.

This necessity of eating after you overate but mis-treated is one of the worst feelings in T1. You know you screwed up and you know you're going to pay for it, because you'll probably spike later and you don't know if it is the big meal you just ate or the snack you ate to keep from going low first. I love pizza, my body hates pizza

You were likely short of potassium too. This is why professional cyclists pack bananas for the ride.

You weren't necessarily hypoglycemic, just low on glycogen. The former is a life threatening condition, the latter is more of a deep exhaustion.

well put. After swimming 10km on a empty stomach that first glass of chocolate milk and a banana were near psychedelic. Obviously not the same life threatening situation as a diabetic but I can imagine there'd be some similarity to the experiences

is this like “the wall” marathon runners are said to experience?

Yeah. Runners call it the wall; cyclists call it "bonking".

I've been told that it can come on more suddenly and acutely for cyclists. As a marathoner I find that I feel it coming for several miles, which is tens of minutes. The activities are somewhat different so it's not impossible that they manifest differently.

But the basic idea is similar. You've got so much readily available glycogen in the body, and when it runs out, you have to shift to a different metabolic pathway -- and your body starts sending up warnings that you are rapidly running out of reserves and must stop now.

It's as much mental as physical at that point.