Days like this I just take a hiatus. If everything's going wrong, and, more importantly, making me miserable, I back off. I take care of other things that need doing. Perhaps I'll decide to plan out a series of blog posts, perhaps I'll design new products, perhaps I'll just craft for crafting's sake, or go out, tidy up, do things I've been putting off.
I totally understand when this stuff happens that you want nothing more than to sit down and just do it all over again to get it done, but if you get stressed over it you'll miss important details. I just turn myself away from it and do something else, and remind myself that the world won't collapse if I let myself take a break, but if I -don't- take a break under these circumstances, I MIGHT collapse, if you get me.