Could be for alot of things, how much did you eat throughout the day before you worked out, how much water did you get, were you sick before you went and worked out?
This is actually less than I usually do, but usually I don't run, I do my cardio in cross country twice a week.
Before I went out to workout, I ate a pack of chocolate oreos, 2 cups of water and 1 cup of soya milk. I don't think it has anything to do with oreos, I eat chips and stuff sometimes before I workout.