Taking the very, very sane person in present time, one would mark a decline of his sanity by a shift from an interest in present time to an overwhelming interest in the future which would decline into considerable planning for the future in order to avoid bad things happening in it; to, finally, a shunning of the future because of painful incidents; to a shuddering and tenuous hold on present time; and, then, an avoidance of both the future and present time and a shift into the past. This last would be a psychotic state.
One holds on to things in the past on the postulate that they must not happen in the future. (A postulate is a self-determined thought or decision.) This sticks the person in the past.