What should you do now?

Slowing down and switching on your hazard lights is the correct combination when you are creating or approaching an immediate danger situation for following traffic, especially at higher speeds (for example on a motorway).

In German traffic rules, the hazard lights are not “I’m stopping somewhere” lights, but “warning” lights. You use them to warn others of a sudden, significant reduction in speed, the end of a traffic jam, an obstacle, or any other situation where drivers behind might not react in time. The key idea is: if your braking could surprise drivers behind you, warn them early with hazard lights while you reduce speed.

Continuing to drive in the clear lane is not enough by itself if there is still a risk that traffic behind will run into you because your speed is suddenly much lower than the flow. Rule of thumb for similar questions: on fast roads, if something forces you to slow down unexpectedly (or you come upon a queue), first reduce speed smoothly and immediately make yourself “more visible” as a hazard by using the hazard warning lights.