In the autumn of 1913 Jung was overtaken, while travelling, by a repeated waking vision of a monstrous flood covering Europe from the North Sea to the Alps, yellow waves carrying wreckage and the drowned. He recorded that he feared for his own sanity, and that when war broke out the following summer he concluded the vision had concerned not himself but the world. The episode, told in Memories, Dreams, Reflections, became the founding case for his tradition's claim that flood imagery can speak for something larger than the dreamer, an overwhelm gathering beneath collective life.
Behind his vision stood the oldest stories the species keeps. The deluge of Genesis, the flood of Utnapishtim in Gilgamesh, Deucalion's flood in Greek tradition, Manu warned by the fish in the Indian: the waters that rise over everything and the one household preserved recur across unconnected literatures, which is precisely why depth psychology took the image as archetypal rather than local.
The working readings are humbler. Interpreters across schools read the dream flood as emotion or circumstance past containment, the banks of ordinary coping overrun, with the dreamer's position, fleeing, floating, climbing or building, read as their current relation to the overwhelm. The folk dictionaries read floods toward troubles arriving in numbers. As ever, these are the traditions' readings; Jung's flood is cited as the tradition's own most famous exhibit, not as proof.