Everything was going great!!! (see my signature) long run 9 miles 2 days ago. My first half is the 26th (10 days away) Today i went out to do a nice 5 miles. IT SUCKED!! My legs never got loose. I had to walk by mile 4 and on and off the rest of the way. My pace was 1:30 off my normal. All I can think is my diet yesterday was Terrible to say the least. Way to many calories and sweets. Any ideas. I thought I was doing great but now Im so sore ...it was not fun....Mike
Started running July 1st 2011
First 5k Sept 3rd 2011 time 34:39
Second 5k Oct 1st 2011 time 30:11
Oct 8th 2011 Mackinaw Bridge 5.6 miles time 56:42
Third 5k 11/24/11 Dork Brothers Turkey Trot 5k Alpena, MI time 27:40
Fourth 5k March 17th 2012 Dork Brothers St Paddy day 5k Alpena, MI 30:25
I'd just chalk it up to a bad day. Everybody has those. It might have been diet, hydration, temperature, humidity, or any of a zillion other factors that affect your run.
Don't let it damage your confidence. If you've put in the training, you've got nothing to worry about. Some days you can blow through a ten miler and feel on top of the world, other days you'll struggle to run 50 feet. That's just the way it goes sometimes.
I agree with the other comments. It is not uncommon to have slower days in training or to suddenly feel exhausted and perform below our expectations. Just know that it is totally normal and is sometimes difficult to pinpoint a particular cause.
My only concern is that it would seem you are going straight from the 5k (with one 8k) directly to the half. That is a big leap, even with a long run of 9 miles, so remember to start out slow and do a walk/jog/run combination as you feel most comfortable.