You got a lot to express out. You had it in your mind the whole day, every moment you kept thinking about it. How you are going to organize it, making it fascinating. How to expand the idea, turning it into an interesting piece of story.
You won't be able to sleep unless you tell it all out. Sometimes, it bothers you so much that you got yourself into frustration.
You sat in front of the blank canvas, thinking on where to start, how to continue and when to finish it.
When all these happen, you know you are in deep shit as you are having a writer's block.
What to do then ?
Shut down the computer and go to bed. Sleep early ! Have a good rest.
Oh, that's so random.