it was inevitable

Last night I had my first "bad run." Bad, I tell you, bad. Out of the 4 miles I was worthless for 2 of them...side stitches, heavy legs, grrrrrrrrrr! Okay, let me give you a little more detail...so you won't think I'm a big whiner for no reason. Well, first of all, Kim and I went to the site of our next 5K so that we could get a feel for the course. A mental thing, ya know. We walked the whole thing...really fast. No, we didn't run it because it was pretty hot AND we didn't want to time ourselves. It's really hard to not check the times. Anyway, it's a nice course with only a few inclines. It looked like it would be an easier courser than our first 5K so we were pretty happy about that. Then, a couple of hours later, my family and I went to Kim's house for a delicious dinner (thanks Kim!). It wasn't a heavy dinner, but I did have dessert...not a lot of dessert, but I guess now that I think about it, I don't normally have dessert. Oh, I also had tea with dinner instead of my usual water. Then a couple of hours after dinner we went home and I put the girls to bed, changed my clothes, picked up Kim and drove to Heather's house for our 4 mile run. I drank water before I left, had my gum to chew, and tied my shoes just right. The first mile was okay, then into the second mile, which is normally my favorite and easiest mile (because it's' mostly downhill) I started with the side stitches. I didn't talk while we ran, focused on breathing more deeply, tried to run through the pain, but oh, I just couldn't. I took a few walk breaks. Then by the last mile my legs were just worthless, although the pain in my side was gone. So, what is up with that? Did I not drink enough water throughout the day? Did the 3.1 mile fast walk earlier in the day fatigue my muscles? Did I eat too much for dinner and dessert? Who knows? Any ideas, all you runners out there? I guess I was due for a bad run, but I'd like to know the reason behind it so I can prevent a bad run in the future.