Normal day fluctuations, either that or some fake news probably floated about. I saw that the Mt. Gox trustee moved around some coins recently. Not sure if they sold them, but that alone could cause enough panic in the market to "crash" it down for the day.
No matter what happened we all know that in the long term the price of bitcoin increase and this time it will increase too so we have to wait for a long term and will get our fruit in the long term. It is sure that the price of bitcoin will increase in this year as in this year many new adopters came to adopt bitcoin and after that the price will increase more because people will prepare for another halving to get the profit from the rising price.