Worst run of your life?

I just had mine yesterday.  I can't even call it a run.  It was about 80% walking. TERRIBLE.

I was so tired yesterday, so idk if that was the problem or what?  I also didn't have my tunes because my phone was low on battery, so that could have been mentally psyching me out.  I wanted to run, but everytime I tried to I had to stop and walk because all of my muscles were so drained.  I even took an energy gel that I had left in my bag after the half marathon to see if that would help- it didn't.  Oh, and my calves were cramping up way worse than they already have been lately.

I kept thinking about sitting down and sleeping the whole time.  Not even joking, I was starting to get a little concerned.  I swear I was nodding off while walking at one point. 

But, not all was lost.  I got my new Garmin in on Friday and I wore it for the run yesterday- that thing rocks!  It is great knowing in real time how far you've gone, what your pace is, and what your course looks like on a map. 

So...what were your guys's worst runs? Has anyone ever experienced super fatigue on a run like I described??