I was wondering what this was all about - but my quick search says Elon Musk seems to be one of the reasons for the decline.
The reason behind the huge dump is the media spreading mislead news about Elon Musk. The media claimed Elon Musk sold his Bitcoin, but no proof about it. I think everyone been deceived by the media and the market is being manipulated by big players. I believe this all the reasons why there is a significant drop in BTC price.