Applejack begins overworking, but she's not working fast enough for her liking. To make things worse, Big Mac had gotten heat stroke. She asks Twilight to mix up a potion that will keep her awake for a complete day. The potion works tremendously, a bit too tremendously.It doesn't wear off after 24 hours like expected. Applejack finds herself unable to sleep at all. As time goes on, this quickly takes a toll on the pony's mental stability — a side effect which bodes disaster for all of ponyville.