So, I was re-watching ROTG and then i noticed something. When Jack touches the dream sand, it takes a form of a dolphinI was interested in why Jack dreamed, of all things, a dolphin. So I went on this website and searched on dolphins and the screen capped it.
My guess is that Jack reflects spiritual companionship. That being the case I would say that his subconscious is showing the real Jack Frost, meaning he is lonely yet contented with life.