I don't understand boggarts

Sure if your biggest fear is a spider or Voldemort or a clown or some shit as shown in the films the boggart can take the shape of those. But there are fears that it doesn't seem like a boggart could replicate. What if my biggest fear is heights? How could a boggart take the shape of "heights"? What if my biggest fear is dying? How can it show death? Hell theres people who experience extreme night terrors so they're afraid to fall asleep. How does it do that? I'm looking for some loose answers because I know JK put little thought into her new introductions and how it would affect the plot. So basically the out of universe explanation is that JK is a terrible writer when it comes to continuity, which you can apply to like 20 things across the series she wrote. But whats the in universe explanation?