I dunno about traumatizing, but the German series Dark (available on Netflix) wound me in a fog of subtle but persistent existential dread that has yet to lift. Wouldn't say it's sadistic, just a few dead kids and minor gore; the real heft of the "horror" is this gradual sinking sensation of powerlessness to escape, nor even comprehend, our immutable fates.

However, it is more of a brooding shifting thinky-think kinda thing, all creep no adrenaline no dash-n-slash. One of my friends watched and loved it as I do, but another thought it was boring, so ymmv.