Some reasons: China banned a bitcoin exchanger, JP Morgan Ceo said Bitcoin is a fraud. Some speculations said bitcoin can go down to 3000$. I think we dont have real reasons to panic. In a few weeks bitcoins price will go up again even higher than it was because thats what happened every time. Bitcoin price have a big fall than it go up higher than it was last time
I have seen the article about JP Morgan CEO, that guy criticize bitcoin from beginning, in 2015 he said that bitcoin will go to zero but look where it is now. How big mistake he made, but that guy still talks bad about bitcoin. His words are just fraud, fraud and fraud, he didn't really explained why, he didn't present any facts and evidences. I don't know how anyone can trust this guy.
Did China banned exchangers? For now speculations are moving the price up and down, and fluctuations are really big, but I also think that bitcoin will go up again and higher then ever before.