I can't think straight. I fight between inspiration and delivery in message. I'm guessing this is the issue for most of us. Just like constipation, some of us will have a regular bowel movement when we stop fussing in the morning and some of us need to go for a brisk walk to effect the same.
Clearing your thoughts may require the element of space and air to get the flow and other times we might need to stop everything we are doing, forget about it and let it come when everything settles down enough for the butterfly to land.
So the formula of expression must be different for each person. Find out yours and eradicate writers block.