I can see a scene in my head, and when I try to get it down...

I can see a scene in my head, and when I try to get it down in words on paper, the words are clunky; the scene is not coming across right. So frustrating. And there are days where it keeps flowing. Open the floodgates, and there it is. Pages and pages coming. Where the hell does this all come from? I don't know.