A bad week for running

I ran this morning for 2 hours... just a slow pace, around 18km... and it was terrible. Now I feel like I've been hit by a truck. Both knees are killing me, my back is locked up and I'm exhausted. Please, please, please don't let this happen on Marathon Day. I had a rotten cold for a few days during the week but I thought that I was fully recovered. Let's just hope this is just a bad day and not a warning for the race. Something is telling me I should rest up for a while, because what we did today was less than half the distance I need to run in two weeks time. Aaarrgggghhhh....