Load the last N deprioritized states will be extracted from the "deprioritized" stash and put to "active" stash.
        N is controlled by 'num_fallback_states'.

        :param SimulationManager pg: The simulation manager.
        :return: None

def _load_fallback_states(self, pg):
        """
        Load the last N deprioritized states will be extracted from the "deprioritized" stash and put to "active" stash.
        N is controlled by 'num_fallback_states'.

        :param SimulationManager pg: The simulation manager.
        :return: None
        """

        # take back some of the deprioritized states
        l.debug("No more active states. Load some deprioritized states to 'active' stash.")
        if 'deprioritized' in pg.stashes and pg.deprioritized:
            pg.active.extend(pg.deprioritized[-self._num_fallback_states : ])
            pg.stashes['deprioritized'] = pg.deprioritized[ : -self._num_fallback_states]