Writing Sprints

Yesterday, I had what I like to think of as a writing sprint. Some days its hard to write a single word. To make my self-imposed word count deadline I have to focus until my head hurts. But, every once in a while, like today, I go through a writing sprint. I cannot get the words out fast enough. I can write 6-12 thousand words in a single day.

I love these days. So much gets done. But what triggers it to happen? I have no idea. Does this ever happen to you? Or can you ever read a ton one day and then not read very much the next?