I've been running off and on for a few years, but several months ago I decided to train for a marathon. I've been running mostly on a treadmill, due to job constraints. I started out running at about 9:30 to 10:00 min miles but then, all of a sudden, I just couldn't keep up that pace anymore.
Have you been following a specific training program with periodic rest weeks? If not, you may suffering from some level of overtraining, though its usually accompanied by loss of interest in training, depression, and/or disturbances in the sleep cycle.
Thanks, guys. I'm going to have to give the dehydration possibility some thought; that definitely could be playing a role. Hopefully after the end of this month I'll be able to put in more time on the street, as opposed to in the gym, as well.
Thanks again