Why do financial (and other) crises (sometimes) cause a recession? Because they increase the demand for money and so cause an excess demand for the medium of exchange.
But why do financial crises increase the demand for money? Because the demand for money depends on the synchronisation of payments and receipts of money, and synchronisation is a system property that requires coordination between individuals, and a financial crisis will disrupt that coordination. Creating a new coordination may take time.
I'm just playing with this idea, to see if it can fly.