Medium-wide: What is a Good Nightmare?

What is a good nightmare? Is there even such a thing as a “good” event that causes you unnecessary emotional distress? We aim to unravel this by going through a handful of films that left me beside myself with anxiety and dread at one point or another. In doing so, hopefully, we can find the answer to the eternal quandary at the heart of every horror fan: why the hell do I watch this messed up shit if all it does is put me on edge?