Unfortunately I think he will always be like that, either on cloud nine, or down in the dumps. Absolutely no one better than him when he is playing well, but if things go wrong he is better off left at home sucking his thumb.
The name that came to my mind too. Knocky didn't have a bad season as such, but his part in the team evolved somewhat. He isn't able to attack defences in anything like the same way as he was in the Chamionship, and his game had to become more defensive, tracking back, harrying defenders etc...