This 'Dark Impulses' book—not sure if you mean the one by that author from a few years back, the translation of that webnovel, or maybe a similarly titled thriller? The one I read centered around a therapist, Adrian, whose own repressed violent fantasies start bleeding into reality when a patient describes a murder eerily similar to one he dreamed about. It's less a traditional mystery and more a psychological downward spiral, where you're never quite sure if he's being manipulated, cracking under pressure, or if some supernatural element is involved. The plot unravels alongside his sanity as he tries to trace if these 'impulses' are contagious somehow, linked to a shadowy online forum his patient mentioned.
What hooked me was the atmosphere, this constant low-grade dread in every chapter. The main plot isn't about a big external villain so much as the internal corrosion of the protagonist's moral boundaries. The ending leaves things pretty ambiguous about the source, which some readers hated but I thought fit the themes perfectly. It’s a slow, claustrophobic read that spends more time in Adrian’ breast voice than on action sequences.