Possessed by an entity

The Enterprise has set a course back to the T-Tauri system. As soon as they arrive, an energy pulse passes through the shields and possesses Counselor Troi while she sleeps, sitting right up, glowing with a green light.

On the bridge, the turbolift door opens and a possessed Counselior Troi enters and is naked. It seems Deanna was sleeping nude and the entity did not dress Deanna's body before leaving her quarters.