What is the right course of action now?

On German highways, the "Rechtsfahrgebot" (keep-right rule) requires drivers to use the rightmost lane whenever possible, except when overtaking. You are only allowed to stay in the middle or left lanes if you are actively passing slower traffic, preparing to overtake, or if the right lane is too congested. Once you have finished overtaking and the right lane is clear, you must return to the right lane. In the situation described, remaining in your current lane (answer 1: "I stay in the middle lane") is allowed as you are either overtaking or have not yet completed the maneuver. This rule helps ensure smoother traffic flow and reduces unnecessary road congestion and dangerous lane blocking for faster vehicles approaching from behind. Always check your mirrors, use your signal, and return to the right lane as soon as it is safe after overtaking.