Yeah, he's sick all right. Poor Sirius.
I love this. This is exactly how one's mind works when one is sick. All this way and that, and something is bad and then good and then bad all along. And you know its just the fever playing tricks on you, but you can't stop it.
I love how Sirius screams for Remus, and they get Remus out of Charms. Poor Remus must have been worried sick when they came to get him.