It was probably the nutrition. What did you eat the night before? How about the day before? Even if the apple and breakfast bar would have been OK (maybe around 200/250 calories?), if you didn't eat much the day before, that would affect you. Have you been a bit on the hungry side lately?

Then again, sometimes, you just have a bad day. There are days where I have gone out and feel like I'm going to die... and other days where I fly along.

You have to figure out what works for you nutrition wise. I will say that cardio on a bike is less jarring and thus easier to consume food before/during, without getting sick or cramps from it.