aggregate demand" is a pretty slippery concept. You demand less of one good if you demand more of another. But how do we demand less of everything? Most "aggregate demand" models are missing a budget constraint. When they do put in a budget constraint, we demand less of everything by demanding more money. That, at least makes sense.
Anyway, Surely something like
"aggregate demand" is at stake in turnining a financial crisis into a
sharp downturn. The puzzle is why it goes on and on.