There are so many different reasons for this. Many of the listed below are good and viable reasons. However, I think, the main reason for the slump is the upcoming fork this November. Many people are panic hording bitcoins and at the same time panic buying altcoins, as their value right now is low. Therefore, all the market action are affecting how the price of bitcoin is. If you are concerned due to the fact that you would be investing or selling, then you should study the market to know which venture you would better pursue.