When Aang lost Appa, he'd felt like he'd lost everything that linked him to a world he'd once known.
Appa was what connected him to Monk Gyatso, to his airbending friends, to his past. He had been proof that a life long ago had been lived by him.
Not only that, Appa was his animal spirit guide, his best friend. They shared a bond so passionate and true that it couldn't even be translated into words.
How could he have let this happen? Why had Toph? At the moment of the disappearance setting in, he had blamed Toph. Why hadn't she stopped those sand benders? She hated Appa! That had to be the reason.
Even though Katara tried to console him, Aang couldn't control himself. Appa, oh, Appa. His best of best friends. His furry friend.
Had Aang failed him? He'd let him down. He couldn't save him, now that he was gone.
Was he gone? Immediately, he set out to find him.
Aang had felt a total sense of helplessness, being lost in a vast, desolate desert with not a hint as to where Appa could be. No matter how he called or blew his whistle, not a thing turned up.
And when the sand benders turned up, confessing their awful deed…Aang lost it. "You put a muzzle on Appa?!" he cried, and lost himself within his awesome power—the Avatar state.
Katara calmed him, and he became a senseless boy. Forget hope, he said. Hope clouds your vision.
Katara turned that around, of course. Katara could always do that.
Even in Ba Sing Se, he couldn't find Appa. He'd lost a part of himself, within the gigantic city, and he felt hopeless once again. Even with Jet's account of the furry creature, turning up with nothing didn't help Aang. Sure, he was alive, and in Ba Sing Se…but he couldn't be found, not yet. Back to searching.
He'd gone on like that, for a little. Missing his bison. Being without his companion hurt him more than words could ever express. He even yelled at one of the brainless Judy's for telling them to stop searching.
Finally, on that fateful day at Lake Laogai, he'd been returned. Descending from the sky, like an awesome, badass bison angel, he'd returned—returned to Momo, Katara, Sokka, Toph, and most of all, Aang.
On that day, Aang had been saved from himself—his angst. He had his buddy back, the proof of his life long ago. He felt as if a part of him had returned to his being, having been long forgotten and lost.
He was saved.
And Appa? After his terrible adventure, do we even have to say a word?