Расея is a "lower class" equivalent of Россия (see here).
Usually when someone uses this word he or she means that something that happened, or some idea, or the way the person behaves is because of "backwoods mentality" - the way people act or think in rural areas: "Эх, Расея!" as opposed to modern ways of doing things.
The word form is imitating the way the people in some provinces speak.
As for origins of the word, according to Vasmer the first occurense of the word is dated 1517. Before that time the word Русь was used.
The word Русь dates back to 9 century, and has Scandinavian origins.