ما هو دعاء الفجاءة؟

There is no supplication called "Du'a al-Faja'ah" (Supplication of Suddenness). What might be meant by it is the supplication that includes seeking refuge from sudden calamities, which is the supplication of the Prophet, peace and blessings be upon him: "O Allah, I seek refuge in You from the cessation of Your blessings, the change of Your well-being, the suddenness of Your vengeance, and all Your wrath."