Put yourself in Toph’s place at this moment. The only thing she is touching — the only thing she is holding onto — is Sokka’s hand. That’s all. She can feel the wind and hear the yelling, but she can’t see any of it. Her world is the world she feels through her surroundings, but right now she can only feel Sokka. So her world is Sokka’s hand, and it’s slipping away.