The current price of Bitcoin is very high because of China's large pump into buying Bitcoins and the fall in value of Yuan. Just today bloomberg stated that China is again preparing to impose curb or Capital controls on Bitcoin by restricting domestic exchanges on sending bitcoins abroad and setting of quotas on how much can be sent. Considering this the price of Bitcoin may stand a chance to fall again.
Although it sounds impractical and impossible to do, this news might be the major reason for sudden drop in BTC today.
that is not really a drop it's like a correction, or manipulation maybe? china is not only conotrolling the mining scene with more than 70% hash but also is contorlling the market with those pump and dump, that you see each day, i believe that one day this might be a problem for the rest of the world, if chinese will be too big and decide to not go with some necessary change like segwit for example