In the following paper, pursuing a lead from Heidegger’s 1937 reading of Nietzsche’s Also Sprach Zarathustra (ASZ), I first claim that the Nietzschean emphasis on awakening the thought and the thinker of eternal return should be read as analogous to Heidegger’s own call to awaken a fundamental attunement in the 1929/30 lecture course, Die Grundbegriffe der Metaphysik (GDM). I bolster this claim by insisting on a Nietzschean inspiration in the very call to awaken a fundamental attunement, which can be identified on both implicit and explicit levels of the text. Initially exploring these levels, I argue that their commonality announces in part Heidegger’s effort to digest a debt of gratitude to the Nietzschean concept of horizon, and the task of the paper becomes to locate and articulate the connection between Nietzschean horizonality and the Heideggerian phenomenon of attunement. This is achieved through the dynamics of sleep and awakening as Heidegger contends with them thematically in GDM. By enumerating key steps of Heidegger’s argument, I show how attunement demonstrates the force of the problem of horizon and with it, the extent to which Heidegger’s thinking can be said to be intimate with that of Nietzsche.