What are some things that make you feel existential dread while reading?

For me, the biggest one that started after breaking this latest reading slump, is that I don't have enough time to read all the books I want. And I don't mean every single book in the world, just how long it takes me to get through a book and getting to the next one. Makes me want to read like 10 books at the same time.

Another one, I believe I can pin on 1 book. Pen Pal by Dathan Auerbach. This book is based on a true story and without spoiling too much, here's the synopsis: In an attempt to make sense of his own mysterious and unsettling childhood memories, a man begins to reconstruct his past. As the games and adventures of his youth become engulfed by a larger story, he finds that it forms a tapestry of unbelievable horror that he never could have expected. Each chapter completes a different piece of the puzzle for both you and the narrator, and by the end of it all, you will wish that you could forget what he never knew.

I absolutely love true crime, but this book unsettled me in such a way because it had you getting the point of view from a child while reading through the eyes of an adult and it made it way more horrifying. And experiencing that innocence while at the same time knowing better was an experience I will never forget.