Run until I drop

I could tell I was a little thirsty in the afternoon, so I tried to adjust for it. I always underestimate what I will need when I am at the office, sitting pretty still. When I hit the road at 5:30, it was about 86 degrees. I caught a nice breeze on First Avenue and didn't start sweating until 3:15 in. I passed the mile mark at about 6:30, and I knew I had to slow down. With 16 miles left, this was no way to start off. Unfortunately, I just didn't do it. I got going. 6:22 pace through 3.35, then along the Mt. Vernon trail I slowed a little and averaged 6:25 pace through a little more than 6 when I turned onto the Four Mile Run Trail. I made a conscious effort to slow down once I hit Four Mile Run, and things got a little smelly along the creek. When I crossed over at Shirlington, I started to feel a little fatigue, but kept pressing. Crossing Walter Reed Road meant I would have some shade while I traversed a few parks, and that helped a little. When the trail starts to descend to water level, though, I typically feel terrible, and this time was no different. About that time my mp3 player, which I was admittedly cheating by using, shorted out. It was dead weight for the rest of the run because I couldn't listen to podcasts to keep me interested anymore. The climb at Glencarlyn Park was miserable, though not as bad as the first time I ran it.
I started wringing out my shirt at this point, and sweat was just pouring out. When I hit Bluemont Park, I was practically jogging. I crossed Wilson and started heading up Alrington Mill, and when I got to the top of the hill I stopped. For a while, I thought I would start jogging again, but it just didn't happen. I wasn't dizzy, but I couldn't spit, there was just no more moisture in my mouth. I shot for 17, got 12.5. Not the long run I had envisioned. I stopped at a water fountain, but it did little to refresh me. I walked another 1.5 miles to the East Falls Church Metro station and rode it home. I had no appetite for the rest of the day, and ate rice and peas only because I forced myself to do so. It was bad.
It also made me wonder about my physical limits. How much longer would I have been able to run if I kept that pace up? In all, I averaged 6:59 pace, though it was surely slower in the second half.
Adjusting to this summer weather (especially once it officially becomes summer) is going to be my biggest challenge.