Dasein, in being applied to the phenomenon of human existence, describes a world that is a world of thrownness and engagement, and temporalised in both its transience and its endurance. As factical, Dasein is being-in-the-world (In-der-Welt-sein); through Dasein, the world is what Heidegger calls “worlding” (das Welten), a phenomenon which happens in and through time. As the world “worlds”, it brings Dasein into this happening, an Ereignis that opens up Dasein‘s own possibilities in its ecstatic-horizonal projection upon the horizon of the question of being (Seinsfrage), which Dasein itself always is. For Dasein itself is a question, never a final answer – that is the meaning of the temporalisation of being.
But death – it “un-worlds”, and Dasein is no longer there (da). And yet, as Heidegger shows in Being and Time, death is Dasein‘s ownmost possibility of being. Hence being and nothingness, life and death, are intertwined – in the throes of ecstatic-horizonal temporalisation which is the lifelong phenomenon of being-toward-death (Sein zum Tode). To be in the world and to be no longer in the world – both are faces of the same head of being as such. This “monstrosity” (“Ungeheuerheit“) in the phenomenality of being is what makes Dasein tremble (zittern) in face of the abyss (Abgrund) of its own inherent nothingness that “un-worlds” at the same time as Dasein itself ceaselessly “worlds” itself in its everyday relationality with the living that forms its own world, and which we call “one’s life”. This is precisely where we can phenomenologically point at the popular obsession with Erlebnis (lived experience) as the closing off of the possibilities of being that death bestows upon us. Death is much more than the ontic being of coldness and rotting; it is the ultimate paradox, in that it is life itself.