Keeping my Sanity

I had a complete story idea

So was busy today, woke up with an idea about magic as currency - which turned into something different.  Ended up writing just over 4000 words on the idea at work (I said I was busy lol), started with just writing the ideas for scenes, which then turned into a plot and had a few characters and sub plots  I have never plotted before, always just write and see where it goes.  Now I am terrified and excited (which makes me feel a little sick), about actually writing it.  I have a beginning, middle and end and no matter what am going to write it.  I have some scenes outlined so instead of getting cold feet am going to start by picking any scene, in no particular order, just whatever one I can really see and hear in my head.  I know it probably won't go according to plan and will (hopefully) take on a life of it's own, having a compete idea is dead exciting though.