An imaginary audience can occupy a room in which you are physically alone.

You are rarely as alone as the room suggests. There is a watcher in your head, assembled from particular people, and you narrate to them, justify to them, and adjust your behaviour for them while nobody is present. Privacy is a physical condition, and it does not automatically produce solitude.

When you notice yourself performing in an empty room, try to identify who the audience is. Naming them tends to reduce their standing considerably. It is also useful information about whose opinion is currently running things.