Bitcoin prices have never been so low this year. Prices were down to 5,826.41$ (Jun 24 2018 16:04:00 UTC). Many advisers say that at the end of the year it will hit 30,000$. The market is seeing more than the fall from the price rise. Imagine when the speculation will end?
In my own opinion, the reason why it was the highest fall this year is because it already managed to reach $20k dollar last december so it was just normal for the price to drop even more right now.