Serious lack of mojo today

I can't get into exercise today. I've had such a great week and I'm certain the scale would agree (Mondays are weigh-in days), but today I just can't get myself to exercise.

I went to the gym to run on the treadmill. Typically, I can easily run a 5K. I made it about 6 minutes into the run and wanted to die. So I stopped, regrouped, and started doing some one minute sprints in the hopes that maybe my body just wasn't cut out for endurance running today. Did that for about 10 minutes, but by that point I was in such a negative mind-space that I had basically checked out. This is the first time in MONTHS that I haven't been able to complete a workout.

I had a good breakfast. Enough protein. The only thing I can think of is that I pushed myself too hard yesterday between a personal training session and then spin class... and my body just wasn't ready to go at it again this morning.

I finally just 'called it a day' with running, and decided to just leave the gym and head home. I'll go back tonight for spin class, and will hopefully be in a better mood (or at least, the people in the group will keep me motivated enough to keep going).

Anyone else have these days? Where no matter what you try, you just can't get it together?