For me they normally happen, these career crises, often, actually, on a Sunday evening, just as the sun is starting to set, and the gap between my hopes for myself and the reality of my life starts to diverge so painfully that I normally end up weeping into a pillow.
And when they leave,they take your life of details with them. You are expected to move on again, but you don't remember what it was that moved you, because no one's asked you in so long. Not even yourself.