Avatar: The Last Airbender Season 3 Episode 9 : Nightmares and Daydreams

The invasion is four days away, and Aang begins to feel nervous about confronting the Firelord. Feeling that he is unprepared, he trains constantly and loses sleep, causing him to hallucinate and have nightmares. After three straight days, it takes the collaboration of Sokka, Toph, and Katara to get him to finally sleep and feel confident about facing the Firelord.