Multiverse (unofficial)

A similar concept to withdrawals can be found in the King's Quest ZZT universe, where Jerrod Wilson accidentally stumbles into the World of King's Quest from the world of Gold Rush while trying to find his brother Jake Wilson, and has to be told he isn't in his world anymore.

In, King's Quest ZZT 2, Da'arda the Bard may also exist on another plane in the multiverse. He talks of Daventry being a far away land, but not charted on any available maps. He says it is unreachable by all known sea ways, paths, or rivers. He is only able to visit via dreams. He doesn't know if the land is only a dream, and states that nobody else knows.

A hole in a rock in King's Quest II: Romancing the Stones looks into the world of Quest for Glory (although this is more of an easter egg).