Your brain doesn’t stop working just because your sleeping or out of commission. It is the ultimate processor and continues to hack away at a problem without your conscious awareness. At the height of my commercial career when an idea just wasn’t surfacing, I would wrap it up and go to sleep knowing I’d have it in the morning. Even with a 10:00 o’clock call and 20 musicians on the floor, I knew that the best move was to get away from it. This can be a scary thing to do at first, especially when there is reputation & money at stake, but try to cultivate a similar work habit. If you force it you’ll just have to do the work all over again because it won’t satisfy the job or will be substandard.
I’ve tried to replicate the work habits of the writers I’ve admired. Hemingway worked early in the morning and wrote standing up at a planters desk. I don’t copy the desk bit but I do work early in the morning and adhere to his admonition to always write until you know where it’s going to go next, then wrap it up for the night. This gives you a starting point when you pick it up again and you’re not staring at the score pad for hours trying to come up with something. Along these same lines, try staying away from the sore pad (or monitor) until you have a concrete idea to start with.
“Start with one true sentence” he’d say and to paraphrase the old man, “My aim is to put down on paper what I hear in what I feel is the best and simplest way.”