I think every writer has moments of inspiration, moments of exciting creativity when the story or the characters take over. The writer might feel as if the words are being dictated. Of course that will be only the first stop for those words, that creativity. Every great writer wants whatever is put on paper the first time to be the final version, but that only happens sometimes. Very often much of what ‘fell’ onto the paper is going to be rewritten and reshaped. In the end those ‘sometimes’ when the words come so fast end up in the same place as the words that have to be extracted from the writer’s mind.
‘Sometimes’ is really all the time and speed is merely a momentary perception