What does "snap out of" mean?

Suddenly recover, as in You can't expect an entire economy to snap out of the doldrums overnight. This expression is also put as an imperative, Snap out of it! telling someone to return to his or her normal state of mind from an undesirable condition such as grief, self-pity, or depression; for example, Snap out of it, Stella; it's over and done with. [1920s]