When. Within the morning and evening remembrance. It is also the supplication people reach for at the height of good fortune, which is precisely when it is hardest to remember.
The words. Four things are named, and each is the reverse of something already possessed. Zawal is departure — the setting of the sun uses the same root — so the first is not the absence of blessing but its going away, which is a different fear entirely. Tahawwul is turning, changing state: the request is not to lose 'afiyah but for it to shift, to become something else. Fuja'ah is suddenness, and it is applied not to the punishment but to its arrival; the word placed under refuge is the timing.
What it assumes. Every clause takes for granted that the speaker currently has these things. This is not a supplication of the desperate. It is said by someone whose health is intact, whose affairs are in order — and it is the possession itself that the supplication turns into a reason to be careful.
The last clause. Wa jami'i sakhatik — "and all of Your displeasure" — closes the list by refusing to be a list. Three specific fears, then the whole category, so nothing is left outside by accident.
Why suddenness. A blessing rarely announces its departure. The supplication does not ask for warning; it asks for refuge from the thing itself, which is the more honest request.
In practice. It is short and reads easily, and it belongs with the ordinary morning and evening formulas rather than in a category of its own.