Writers call it many things: finding your muse, getting in your zone or trance, stepping into the plot...
However you see it or feel it, you are transported to another place that's of your own creation to spend time with people you are getting to know as they reveal themselves to you. Stephen King calls it magic, and who can disagree with the master of fiction?
When I'm there, inside the story, with my characters, I find my job is to write it all down as I share the adventure. Later, the work begins of getting it all in order.
Don't be afraid to get lost in your story. Float along as the story flows. And enjoy the magic of the process.