I... tip over.

Nearly all of my falls can be attributed to "didn't eat lunch" combined with "went biking". I'll get lightheaded, stop tracking basic things like "is there traffic", my legs will turn to jello... So I try to stop, because in that state walking the bike is a *good* idea. And then I fall over in slow motion. I have learned that this is a bad combo, so now I'm making myself sandwiches before I ride, or starting out early enough that I can grab a sandwich while out.

What you're describing is similar to what happens to me on a day where I try to ride even tho I've overdone it for the week.