I went through a period of a couple of months where I couldn't do anything right. Even the simplest things took me forever to get, and everything that I had been reletively good at had deteriorated. My ukemi, which had previously been very good, was terrible, and every throw I took hurt. I was off balance, more than once falling down when I was nage.
And everything I did to correct it just made it worse, and I started to get an anxiety about going to class. It passed. It always passes. My sensei often tells the stories of the times he's wanted to quit. Anyone going through this should be confident that s/he will get past it. The thing I found that helped me get over it, though, was relaxation and centering myself. I was worried about screwing up before every class, which made me tense. No sense of center made me off-balance. I didn't consiously relax or center myself, but one day things started clicking again, and I found that I was relaxed and centered. I think that the most important thing that I did to get over it was that I kept going to classes, even though I was starting to hate them. Had I quit, I would have never gotten through it.
If you're in a rut, I hope you get out of it.