What caused the collapse?
Just think about it, less than 24 hours ago, it was possible to sell the BTC on a thousand dollar higher. Probably, it is impossible to define why “the foundation was cracked” under the cryptocurrency, as for the example it can be done in a regular market. In the digital, the effect is first  seen and only than the reason becomes known.

Reason #1: Contagious effect
Reason #2 : Direct correlation
Reason #3: Global Bitcoin influence

What should do the owners of cryptocurrency: sell or wait?
It depends on the inner aspects of each owner. Even when the course is rising – it still have cycles of fall.

https://thecoinshark.net/three-hellish-days-for-cryptocurrency-reasons-of-the-fall-of-the-currency-and-what-to-do-next/


This is a good article to understand what is happening.