That big dip is due to Big news like china put ban on ICO's and Some negative Statements from JP morgan CEO , all these added together and panicked people. But bitcoin Recovered instantly as if it never went down..
But i suspect , some big guess wanted to buy bitcoin at really cheaper price, so played some tricks to bring the price lower...

This happened after the Bitcoin Cash fork, But to be realistic price went even higher after the fork, from about $3000 to nearly $5000, the dip had nothing to do with the fork.
I think even after segwit2x, price will go even higher, as people get free segwit2x coins , they sell them and rush to buy more bitcoins. this may drive price even higher..