Welcome to English in a Minute.In American English,when someone respond to you by saying,"In your dreams!'does he mean that you're actually dreaming?
A:Guess what?This weekend,I caught a fish this big.
B:No way.Yeah,It was huge!In your dreams!There's no way you caught a fish that big.
"In your dreams" is a different way of saying,"I don't believe you" or "there's no way that's true." It is a way to tell people that you think they are making up a story.And this phrase is used in a playful manner,usually with a smile.
AH! "In your dreams" "In your dreams" "In your dreams".......
And that's English in a minute