What is Amnesia: The Dark Descent

[Power_Infinity]

I really love the subtitle "The Dark Descent". But Amnesia I'm not sure about. A great many games these days fall back on amnesia as a crutch for getting the story started. Surely there is a better means of getting the main character where he is to start the game? If amnesia has nothing to do with the main character's introduction into the story, then it would be a fine name.