this time I can't understand where is the bad news behind this big dump

probably some big whale just empty their big wallet?
who knows but right now from a bigger value over 19k on coinbase we are touching a strong defeat

in 2018
There doesn't need to be any bad news in order to trigger a selloff. If the big boys behind the scenes decide to sell their investments, it will happen regardless if there are good news/bad news circulating around.
As for the recent price movements, there is indeed a resemblance on the pattern of the 2014 scenario after all the craze had died out on the 2013 ATH. But right now, the recent crash seems to exhibit some form of life around it compared to the 2014 crash which is followed by 2 years of stagnation. Support levels are @ $5500 and $5000 being the stronger of the two, and if those support levels are broken, all I can see is a reenactment of the 2014-2016 stagnation where it's a stalemate between the bears and the bulls. This is certainly not a dead cat's bounce--not yet.