Sometimes, I have an off day. When this happens, I can't do as well as I normally do in martial arts training (ie, I get tired more easily), but the best thing to do is keep pushing myself anyway.
Usually, the worst things that happen to me are something along the lines of "I wanted to do (insert interesting thing) here, but due to unexpected shit happening and ruining my plans, I can't do what I want to, so now that I have nothing to do, I'm just going to be bored and piss time away."
Worst case scenario, my life is boring, but comfortable. I have it pretty well off.
If you really feel like shit, I'm gonna have to pull an Ares Tyr here and recommend that you take up martial arts.