Back in the saddle?

I always think dehydration among one of the first weird things to make me tired unexpectedly. Did you drink enough? Did you run at a hotter time? If none of those apply and it doesn't happen again I would chock it up to something weird like...oh..female hormones and not worry about it. By the way...I'm Sarah Pachev, the wife of the guy who runs this blog and we are thrilled to have you here. Happy running!!

Another possibility may be sleep depriviation. Without knowing how much sleep you get on a regular basis, I know from personal experience that when I do not get enough sleep, my runs are affected. Not only that, but the rest of my day is negatively affected, even if I run in the morning, which usually has the effect of brightening my entire day. Another possible thing to look at is your diet. If you are not getting enough of the right kind of foods, or perhaps not getting enough vitamins, these would be things to look at also. I finally bit the bullet and decided to start taking a daily vitamin. Good luck, and listen to your body. Overdoing it is a good way to head down the path to injury (I should know, I have done it far too often).