Nothing happened to Egypt. It's some legend of mythic proportions. When you read the Egyptian text of that era, they record no anomaly. They're just counting cattle and grain and keeping track of hostile neighbors. Nothing happened to the Pharoah or his family. The only event they mention is an invasion of an unknown enemy, who they call the Sea People.
It's more likely that a band of Hebrews came into Egypt seeking fresh water and fertile soil and were forced out, leaving them with a case of sour grapes. There was a Hebrew settlement on Elephantine Island, in the Nile, which may have something to do with the source of the legend.
The Bible contradicts history if read literally. This is one of many examples.
Note also, the Book of Revelations appeared hundreds of years after the Hellenization of the Jews. It's entirely reliant on myth and legend, and contains little, if any, text that has any basis in fact or reality.
