He seems to rev up between his emotion states based on incoming DPS on him. If you keep it very slow DPS, he seems to toggle back and forth between calm and upset. Upset being the very mild damage shields and feedback which groups should have no problem handling. If you push too hard on the dps he will increase to worry and then panic, both of which are more or less untenable to heal through continuosly. Take the fight very slowly and you should be fine.
Also, for what it's worth the damage shield values on the deadly mirror (panic) phase don't seem accurate. My paladin took 50,000 feedback multiple times and during the same phase was taking 6,000 melee damage shield.