Hello 2018 First rule to crypto!
DON'T Panic! HODL and remember each time in 2017 when bitcoin fell 6-7 times , it bounced back.
Never sell low! Or at a loss! I learned my lesson in spring/summer of 2017 I sold 1000ltc at $16+- and not only lost my holding to a small fiat amount, also lost 50-60% of the funds when the old BTC-e exchange fell as the founder was targeted and arrested by law enforcement.
This has got me to start collecting and saving my daily change for future litecoin savings.