I have heard different things; 1. people sell out to take profits so that they can have a nice Christmas, 2. smart money coming in is playing with the price, 3. an exchange in asia broke down and caused fear.
I am !!NOT!! saying that either of these three is the reason, I am just trying to get other perspectives for what people have heard cause (could have caused) the dip..
As for me it is clear thing that cryptocurrencies were overpumped. I am telling first of all about Bitcoin. Advertisement, information distribution, high demand and positive forecasts made the whole this thing.