Muscle fatigue while training

Question
Hello,
I am training for a half marathon which is next week. I've been on good schedule recommended by a couple of organizations. Last week I ran my final 12 miles. That was a week ago and it went okay, but I was tired when I started the run and now a week later my muscles are like lead. I can barely run at all. I'm getting concerned about being able to run next week.  Any advice before I run the half marathon to feel better?

Answer
I guess I'm going to answer and criticize more than what you asked, but I can't help but note on two problems that have caused you to feel in crappy condition before race day.
The first is over training.
The second is not keeping yourself active on your rest week before the marathon. You MUST keep your mileage close to your training mileage. Too often people take extra measures to make sure they have enough recovery, and end up being TOO recovered, more specifically, out of shape. You may find that you have faster times and your legs don't feel like pillars during your training week. This is how you want your legs to feel on race day. This is because although your muscles aren't fully recovered, they are still in awesome shape. Do whatever you can to keep your legs in shape.

You shouldn't feel sore after that 12. Okay, maybe a little sore, as you should be after your long runs. But if you are feeling a lot of muscle fatigue, all that means is that you aren't training for that kind of distance, you have more work to do. If 13 miles is what you are training for, you need to be able to run it every once in awhile without the distance killing your legs. Not only that, but the fact that you feel really tired before your runs, you need to make sure that this 12 miles wasn't too much of a stretch for you, and watch out for over training. It is awfully easy to do.

But to answer your question, for now, you need to recover as much as you can, but make it active recovery. If you don't do any jogging or swimming or jump roping, your legs are going to feel like pillars on race day, believe me. Light jogging will do wonders in the aide of recovery; don't be afraid of it. Go to HEB, they sell this liniment oil in a little orange box called Dr. J.H. McLean's Volcanic Oil. On race day, massage your legs with it. It loosens them up, and relieves muscle fatigue.
Good luck with that half.
Jared