A variation on the word doppelganger (a ghostly double of a living person, especially one that haunts its fleshly counterpart).
A doppelgambling is making a bet you dreamed doing, that is, making it in the real world.
X: "What are you doing later Bro?" Y: "Going to that joint on 72th... had a dream about lottery numbers." X: "Ahhh... doppelgambling."