I'm sorry to tell you that no one can give you the exact reason for the fall. Remember that bitcoin is a speculative asset, and as such everyone around the market can sell/buy or trade causing the price to goes down/up. Also its volatile, so it fluctuates based on supply and demand. Again, we don't know what will happen in the future, so its 50/50. But as of the moment, we can all speculate that we might not get that all-time-high this December. We have been struggling for the past 8 months and I believed it will continue up to the end of the year. So don't expect any highs, and be prepared for the worst.