I think the four-letter-word you're looking for is BONK! Maybe not a weave-all-over-the-road-until-you-fall-off-your-bike-and-can't-get-up bonk, but I'd say you definitely ran out of gas. You should bury a Lindt Sur Fin chocolate bar in the bottom of your bag. It's handy for when your body taps out but you're 20 miles from home.