We all have good days and bad days. That applies to coding and may even be exaggerated there. At least my observation has been that the difference between a productive day and a not so productive one can be almost an order of magnitude.
In most languages I will still write code on the not so good days, just not as much. With Lisp however, on the bad days, I don't write a single line of code. And if I do, I discard it the next day. Do you have that same problem? If yes, any theories on why that might be?