did Critchley take the Landmark Forum?

if so, then it does help to get what SZ is all about.
Heidegger's claim earlier in Division 1 of Being and Time...is that the human being finds itself in a world that is richly meaningful and with which it is fascinated. In other words, the world is homely (heimlich), cosy even. In anxiety, all of this changes. Suddenly, I am overtaken by the mood of anxiety that renders the world meaningless. It appears to me as an inauthentic spectacle, a kind of tranquilised and pointless bustle of activity. In anxiety, the everyday world slips away and my home becomes uncanny (unheimlich) and strange to me. From being a player in the game of life that I loved, I become an observer of a game that I no longer see the point in playing.

What is first glimpsed in anxiety is the authentic self. As the world slips away, we obtrude. I like to think about this in maritime terms. Inauthentic life in the world is completely bound up with things and other people in a kind of "groundless floating" – the phrase is Heidegger's. Everyday life in the world is like being immersed in the sea and drowned by the world's suffocating banality. Anxiety is the experience of the tide going out, the seawater draining away, revealing a self stranded on the strand, as it were. Anxiety is that basic mood when the self first distinguishes itself from the world and becomes self-aware.

Anxiety does not need darkness, despair and night sweats. It can arise in the most innocuous of situations: sitting in the subway distractedly reading a book and overhearing conversations, one is suddenly seized by the feeling of meaninglessness, by the radical distinction between yourself and the world in which you find yourself. With this experience of anxiety, Heidegger says, Dasein is individualised and becomes self-aware.