I would have a flick of fear, as in a dream when you find yourself in the wrong building or have forgotten the time for the exam and understand that this is only the tip of some shadowy cataclysm or lifelong mistake.
The quote from Alice Munro's "The Love of a Good Woman" evokes a sense of anxiety and disorientation, akin to the fear experienced in a dream where one realizes they are in an unfamiliar place or have missed an important deadline. This fleeting moment of panic serves as a metaphor for deeper, more profound realizations about life and the potential consequences of one's actions.
This feeling of dread symbolizes the underlying worries that accompany significant life choices. The metaphorical "shadowy cataclysm" suggests that minor mistakes may lead to more considerable, overwhelming repercussions, revealing the complex interplay of fear and regret that can shape our existence.