You're definitely right on the count of psychotic episodes on and the strength. I think then I was just looking for another reason for him to dread the oncoming of the fits. But when I look at it again, the lack of air from that much laughter as well as the breaking of his jaw is probably reason enough.
On the part of the sonic attack, I did a bad job on explaining that. It isn't really an attack, simply the volume of the laughter, the adverse effects of which are just as much a toll on him as everyone else in the room. It's also the force of the air pushing its way out with such force that breaks his jaw.