Flabbergastation is a unique word that is not particularly common in modern language. If you are looking for alternatives to this term, consider using expressions such as astonishment, amazement, shock, or surprise. Other synonyms include bewilderment, incredulity, stupefaction, or dumbfoundedness. Depending on the context, you may want to use words like disorientation, confusion, or puzzlement instead. Additionally, you could consider using more informal language, such as "mind-blowing" or "jaw-dropping" to convey a similar sentiment. Whether you are describing an unexpected event or simply trying to convey a sense of awe, there are a variety of synonyms that you can use in place of the word flabbergastation.