In my case I think it's just natural madness. I've always created narratives, As a child, even when playing alone, there had to be a story. I invented characters, had dialogue with them, had adventures. "You're doing it again!" Mum would say. "Running around the garden and the tenfoot talking to yourself! What will people think?" I wasn't talking to myself. I was talking to my company of valiant knights, daring explorers or loyal soldiers. But I got a thump and was made to play with a ball or something 'normal'.

Later on, I wrote the stories down, rather than acting them out. Every so often, Mum would gather up the sheets and sheets of lined A4 covered with my untidy scrawls and bin them. Protests brought blows, so in the end I contented myself with pretending to read while spinning my own tales in my head.

Many, many years later, my son commented that Wolverine would have had a lot less trouble with the Basilisk than Harry Potter did and that gave me a start with fanfiction. Now I have three different 'worlds' I write in.

As for original fiction - I get inspired by odd phrases like 'black unicorn'. Thoughts about 'different' life-forms and how they might or might not relate to humans. Random thoughts and images trigger things. But very little that I write satisfies me, and the Delete button beckons.