question for the masses

Have you guys ever had a character come to you and he/she HAUNTS you?

Their story is slowly unfolding in small puzzle pieces and you're wondering what goes where and does this little piece fit into this one and if this one goes here, how will it impact that there and sheesh, what's the end result of this huge mess going to look like?

You've got all these questions swirling around in your head and man, the character is cooperating answering them as fast as they can and you can't decide...is THIS the one that becomes THAT story?

Is this the one that will allow you to make the jump from fanfic writer to a writer of original fiction?

I'm enamored by this character. This character is broken and jaded and scarred by something in the past and I just can't DECIDE if the character wants to have their story unfold in the SPN world or in a world of my own design.

So. Like I said, I've got these scenes in my head and I was wondering about YOUR process when you get a story idea.

Do you just fly by the seat of your pants and write or do you plot and write scenes using notecards and try and make the puzzle pieces fit into a complete picture?

Do you use a computer program or an old tattered notebook?

I'm genuinely interested.