Just because of some people's Panic selling.here i should mention media again! Lot's of media publish article about negativity of bitcoin. Some people Trust it. And they had start panic selling. That's why it rapidly going down.
Yes, panic selling will contribute such abrupt lowering of bitcoin price and that is merely because the more people sell the more its supply in the market affecting its price and it is just an indication that there are more selling than buying activity and I think another factor is the whales activity they can manipulate such pumping and dumping of bitcoin for they are holding a bigger portion of bitcoin.