Last night I spoke in a demon voice and acted in a scene by myself, taking my own orders on what to do next.

It was an improv assignment. Inner Demon Voice.

The scene worked out well, even though I had no idea what was coming next. I tied in a twist ending, even.

Instinct is good. Instinct makes us smarter and stronger than contemplation, often.

Good improv lesson: don't think. Do. Right now. Logic works itself out. It's true for writing.
Give it a try.