There is plenty of research that points out that any stress will reduce our problem-solving abilities— and our creativity.
Thinking about publishing, sales, how much you have to write in the next week, what your editor is expecting and your own perfectionism and virtually any expectations will torpedo your work.
Even Einstein admitted that he mostly played at work, imagining and performing mind-experiments including imagining what it would be like to ride on a light beam which formed the basis of his theory of relativity.
People do better when they pretend they are writing a story. Or role-play that they are a famous writer composing the story. Anything that moves the story into play or fantasy will work.
Playing with your characters, playing with the plot, playing with the scenes and settings, taking time to wander around the story and see what is happening…
This is why children are so wonderful at making up stories. It is all make-believe and fun.
Picasso said that he had to unlearn everything he has learning about painting and drawing after the age of 5. I suspect that is true to all of us.