Caludia,
When i hit mental blocks, I tend to evaluate my routine to see if I am in a "rut" somewhere. Usually I am, somewhere in diet, exercise, sleep or fun (i.e. "self-maintenance") and I will make an immediate correction. This happens to me in the winter more frequently because I won't be able to get miles in with the dog. I fix "short blocks" with increased both in intensity and duration, preferably outside.
Good luck!
Harry