... Avatar state. You see, the Avatar State requires huge amounts of chi, more than one body, even an Avatar, could produce. So, in order to generate the power necessary, the body draws in chi from all around. Aang has spent so much time in the Avatar State, that even in his normal state, he is constantly drawing in chi. His illness is caused by his body not able to process all of that chi. It is trying to sweat and vomit it out, but it's not enough."
"So, how do we cure it?" Katara asked anxiously.
"Well, the good news is that it will wear off in about another week."
Katara sighed in relief.
"The bad news is that it will have killed him in about 4 days."
"WHAT! WE CAN'T LET THAT HAPPEN!"
"The only way to stop Aang from dying is to have him lose so much chi that his body will be able to make it through the week without overloading, and the only way to do that is to have him constantly expend chi faster than his body can produce it." Iroh explained. "So, he just has to bend a bit?" Katara asked. "No. In Aang's present state, he is physically incapable of bending, plus even if he could, the action would only slow the rate of chi gain, not stop it, and that's not enough. There's only one way to save Aang's life."
Iroh bent forward to whisper his secret knowledge into Ka...