Never heard it before, but I think the "sudden loss of consciousness" would apply. A slow, steady decline would be "under control" in a sense, but when someone swoons, she tumbles, or drops quickly, out of control. "Collapse" is a word that comes to mind, as applied to a person who suddenly faints, or to the twin towers on 9-11.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.
akdomWith the housing market in a funk and prices swooning,The prices are feeling faint (!), starting to lose consciousness (!), and feeling weak in the knees (!). It won't be long before they hit the floor.