Pull the chute and call it a day.
i've had days like that too. it's like your body just quits and your mind can't do anything about it! if your mental motivation is high, then you can restart, but if not, it's prob best to just put your feet up and give your baby a hug :)
Yeah, my body was still doing okay, but from before the race even started, I just wasn't having any fun, and it just didn't feel worth it to continue. I think I needed this to finally get over marathoning :)