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.