The saying goes that a writer is a world unto themselves; a world or worlds trapped inside one person. I agree with this. There have been times when I have been oblivious to writing, or even thinking about any WIP and an idea will just pop in my head! It’s almost like something out of a cartoon! They just appear!
But what I do now, what I try to do most often, is write the thought or topic down. That way, since it’s recorded, I can’t lose it.
This is what I like to call ‘catch and release’.
You acknowledge the thought or idea (catch). You then write down the thought (release). Don’t fool yourself to think that the ideas that come out of the ether will come back to you with the same speed! You have to be observant and willing to entertain (read: honor) the thoughts that come.
Writers use words as weapons. Pens are our arsenals. Go to war with the pages. Pick up the pens.