It just so happens that I am one of those people that don't sweat very much. So just take a chill-pill, people.
Today I ran 3.1 miles. As I was getting ready to go change into my running clothes, I realized that I didn't eat an hour before, like I had been on my previous runs. The last food that I had was a bowl of Multigrain Cheerios almost 5 hours ago. Drat! So I wasn't as prepared as my previous runs and I really could feel it the last mile. I started out pretty strong (for me, strong is 8:45 - 9:15) and kept it up for the first half, but then got progressively slower until I looked down and my pace was 10:40. Ugh.
P.S. I love Nike+, but no matter how many times I try to calibrate my sensor, it doesn't track my miles accurately. So my pace and miles completed are faster and farther than I really go. I love my Garmin.