What disasters do is shut down the functioning of both the markets and the government agencies.
"Disasters overload political systems by multiplying societal demands and empowering new groups on one hand while disarticulating economies and disorganizing governments (as well as revealing their organizational, administrative, and moral deficiencies) on the other." (A. Cooper Drury and Richard Stuart Olson as quoted in A Paradise Built In Hell, Rebecca Solnit, 2009; page 152.)
After a disaster, the people are for a moment left to their own devices to discover for themselves the possibilities of mutual aid, which is another slant on gift exchange.
That shut-down could also occur during the sabbatical year. With markets and government agencies shut down the people can begin to discover their own capacity. It's not just the land that needs to lie fallow and refresh, it's the human ground as well. During the sabbatical year the political ground of the society can reboot at the grass roots level.
"In the immediate aftermath of disaster, government fails as if it had been overthrown and civil society succeeds as though it has revolted: the task of government, usually described as 'reestablishing order,' is to take back the city and the power to govern it, as well as to perform practical functions – restoring power, cleaning up rubble. So the more long-term aftermath of disaster is often in some sense a counterrevolution, with varying degrees of success. The possibility that they have been overthrown or, more accurately, rendered irrelevant is a very good reason for elite panic if not for the sometimes vicious acts that ensue." (A Paradise Built In Hell, Rebecca Solnit, 2009; page 152).