Same thing happened to me yesterday on a hill I've gone up many times, though it's real tough ( one half mile but double digit percentage). Here in NYS it has been hazy, hot, and humid these last few days. I totally bonked on this hill- analyzing it later made me think it was more heat related than low blood sugar (which might have been a factor as well, since I was shaking). I do not do well in the heat. I usually give up running in the summer and concentrate just on biking because it is just a tad cooler to be on a bike than to be on foot.