By the time you noticed it, it was too late: the story had already begun to insinuate its tentacles through your brain.
You never knew how the story had been spawned: it had simply appeared. Small and misshapen, little more than an embryo but nevertheless stretching out, trying to grow.
Where it resided, you could not say precisely. Its living network eventually extended into every part of your brain, hidden in the mass of your subconscious. Only fleetingly could you sense the flow of memories, feelings and sensations as the story fed where it would and seized what it found useful.
As it grew, it extended itself further and further into your conscious brain, demanding resources, looking for syntax, form and meaning. You cooperated with it, believing it to be a developing child rather than an unbidden parasite.
When it was time, the story pulled itself entirely into your conscious brain, awaiting birth. You committed it to the page and exposed it where others might be infected.