A flood in a dream usually reflects emotions that have outgrown their usual container -- feelings you've been managing that are now simply too much to hold back. Watching the water rise from a distance can mirror a slower buildup, while being swept up in it often names a sense that control has already slipped away.
Mercury in the sixth house of a nativity, the native shall change from one religion to another, & will have his felicity in part impedited by reason of his inconstancy. - William Lilly (1602.-1681.)