It's not story hour fatigue, but sometimes I just can't get into the kick of writing. I found that I have a mantra that helps out.
"It doesn't matter what I write. I am just putting words on paper. I have no goals. I am simply seeing what forms. I have no concerns of quality. I'm just using up some time. Whatever I do will be great, because I have no expectations. And even if it isn't great, it doesn't matter. I enjoy the act of writing. I have no need for the outcome."
And I write like that, usually a paragraph or two. Which, by that time ends with, "But as long as I'm going to be sitting here for the next fifteen minutes, I could be writing about X..."
Once all the worry starts to fade away, once I get past that squirming little twisting need to get up and stop working because it might turn out badly, then I can write. It's especially useful if I've got a product proposal, or update due for work.