First Off. Buy the dip, we have been blessed with prices this low and if you can get in now you will see great gains over the coming weeks. Ok, Bitcoin has fallen to the low 4000s and is even trading sub 4000 on Okcoin and other exchanges. This is mainly because of the regulations that Russia will be putting on the exchanging of bitcoin. Another reason that it has fallen in price is because of the constant strain that the Chinese government is putting on cryptocurrencies and Bitcoin. However I do not think this will last long, especially because of the development of decentralised anonymous exchanges that will allow people from all over the world trade Bitcoin and other assets, without government regulation or fear of shutting down.
Sources:
https://www.forbes.com/sites/kenrapoza/2017/09/08/russia-faces-internal-battle-over-bitcoin/#3ffb7e73207e
https://www.reuters.com/article/us-russia-bitcoin/russia-to-regulate-bitcoin-market-finance-minister-idUSKCN1BJ1WB
