What should you do now?

Both "I slow my vehicle down" and "I switch on my hazard lights" are the correct actions in this situation. In German traffic, when you approach danger or encounter a situation that could surprise following traffic—such as slowing down due to an obstruction, sudden traffic jam, or any unexpected event on the highway—you are required to reduce your speed and warn others by switching on your hazard warning lights. This helps alert drivers behind you early and can prevent rear-end collisions. Continuing to drive without slowing or signaling could put you and others at risk. These rules ensure that all drivers are aware of potential dangers ahead and can react safely.