Revelatory happening (3-6)
(Other definitions for eye-opener that I've seen before include "A startling enlightenment!" , "Something startling" , "Fact that brings great surprise - wakes you up" , "Circumstances that brings surprise and enlightenment" , "Surprise revelation" .)
(Other definitions for eyeopener that I've seen before include "piece of information that's surprising" , "For Uncle Sam, perhaps hair of the dog" , "revelation" .)