"Physiology" is fundamental to Nietzsche's understanding of the human. I pose the question of how the death of God, the modern event that fundamentally alters the Western human being, can be understood physiologically. The death of God, I argue, is triggered by modernity's awakening of a physiological awareness that Christianity had suppressed, but God's death in turn catalyzes a physiological crisis: the unfettered exposure to limitless new possible values, data, and paradigms, no longer regulated by the strictures of faith, overruns the capacities of the finite, embodied human, in nihilistic modernity. Since, for Nietzsche, physiology is the study of the will to power realized as drives, the death of God and of Christianity must be understood as the death of a certain epoch of desire. I read Nietzsche’s new divinity, Dionysus, as the figurehead of a new desire in humanity, the desire for the always-already-departed source of being – namely, “Becoming.” Nietzsche’s ultimate decision to define Dionysus as the “unnameable” and necessarily “unknown” god that is more-than-Being complicates his relationship to Christianity, inviting us to read Nietzsche’s thought as a hard struggle to overcome Christian thinking, rather than an easy decision to do so. Physiology is the name, I ultimately argue, of the mode of thought that can overcome metaphysics.