In addition to the other comments about relationships, there is a line which alludes to fade, which Sia infamously rejects.
"It's lonely at the top, blackouts and airplanes"
"At the top" refers to fame, so Sia is simply saying fame is lonely. She has also been quite vocal of her dislike of touring, which takes a toll on her health. This is what the airplane could refer to (constant travelling for other people and not necessarily yourself).
In addition to the other comments about relationships, there is a line which alludes to fade, which Sia infamously rejects. "It's lonely at the top, blackouts and airplanes" "At the top" refers to fame, so Sia is simply saying fame is lonely. She has also been quite vocal of her dislike of touring, which takes a toll on her health. This is what the airplane could refer to (constant travelling for other people and not necessarily yourself).