The Chinese government banned ICOs. Naturally as a result, alt coins started dropping. People are fearful they won't be able to get their money out with the government cracking down.
For the next couple of days I think it will blow over and go back up, but only time will tell.
This is the fundamental explanation, sure. But it's just like when news teams try to explain every rise or drop of a stock price with fundamental news. Sometimes the answers are more technical and related to supply and demand. We hit a major psychological resistance ($5000), and it's entirely possible that supply began to outweigh demand.
The FUD around the Chinese ban on ICOs may have catalyzed another leg down last night. But many technical analysts will tell you that this leg down was going to come either way.