This is what happened to me -- 25 years ago to the month -- when I wrote the text for the hymn, "Lord, I Would Follow Thee."
I had been writing for various church programs for more than 10 years, including song lyrics for several seminary projects. The "new hymn book" was a slow, unwieldy possibility that had been dragging along for five years or so. Michael Moody, the gentle, insightful man who for many years headed Church Music, would make a point of inviting me to submit texts for this new hymnal; indeed, every time our paths crossed, when I was working on one project or another, he would encourage me to do so.
I would go home and two very unusual things would happen, consistently so. One: I would attempt to write, but nothing of any merit whatsoever would emerge. Two: I would then promptly forget, the whole idea simply slipping out of my mind.