Being astonished in a dream is read as the unexpected breaking through routine. Dream books link it to openness to change and to news or insights that arrive from an unforeseen direction.
Has this come up in your dreams before? What was going on in your life then?
My Cosmic Code has a private dream journal. Write a dream down and the app picks out the symbols in it, shows what dream books say about them and, over time, which words recur across your entries. The journal is stored on your device only.