Anxiety in the face of death is anxiety ‘in the face of’ that potentiality-for-Being which is one’s ownmost, non-relational, and not to be outstripped. That in the face of which one has anxiety is Being-in-the-world itself. That about which one has this anxiety is simply Dasein’s own potentiality-for-Being. Anxiety in the face of death must not be confused with fear in the face of one’s demise. This anxiety is not an accidental or random mood of ‘weakness’ in some individual; but, as a basic state-of-mind of Dasein, it amounts to the disclosedness of the fact that Dasein exists as a thrown Being towards its end. Thus the existential conception of “dying,” is made clear as thrown Being towards its ownmost potentiality-for-Being, which is non-relational and not to be outstripped. Precision is gained by distinguishing this from pure disappearance, and also from merely perishing, and finally from the ‘Experiencing’ of a demise.
Martin Heidegger, Being and Time