Mark 9:26

Mark 9:26. And the spirit cried, and rent him sore, and came out of him: and he was as one dead; insomuch that many said, He is dead.

As old Thomas Fuller says, the devil knew that he had to go out, so, like a bad tenant, he did all the mischief he could before he left. Satan often acts in this fashion; just when Christ has come to cast him out, he drives the poor soul into deeper despair, and perhaps into greater sin than he ever fell into in all his life before.