You know what the saddest song in the world is? A Dream That Can Last by Neil Young and Crazy Horse.
One of the more uplifting songs in the world is The Cave by Mumford and Sons. And don't forget Just Breathe by Pearl Jam. Don't Give Up by Peter Gabriel and Kate Bush too. I think you need at least three uplifting songs to cheer you up from the saddest song in the world. Though listening to the saddest song in the world can actually make you feel better, too, in a weird way.