Rod Serling (the creator of The Twilight Zone) said that writing is incessant, and demanding–and he succumbed to it. This is the best way to describe this entity, this power, this source knows as The Flow.
It is this need to create that is indescribable–this feeling that you as a creative person to pull out what is in your head, and put it on paper. Or on canvas. Or film. It is the feeling (it definitely starts as this), this unction that is pushing you to create, forcing you to create. I feels like all creative channels are open and anything that can be created, will be. The great thing about The Flow is once you have experienced it, you will never be confused as to what it is!
Think of it as a teapot. Your talent is what fills it. Time and effort heat the water, and when it whistles? That is your queue to create. That is your signal that you are sitting on something amazing, that you have the amazing on the inside of you–and you should believe enough in yourself to do access it, in order to bring to life what is already living on the inside of you.