Firstly; There is nothing like a flash crash; in crypto currency if you are very good in trading, and evaluation of market situations you would understand that any slight dump in bitcoin leads to a corresponding massive dump in etherum because all (96%) tokens; all (96%) altcoins are paired with ETH Pair; while eth is paired with Bitcoin.
Fundamental and Technical analysis has predicted that there will be a price correction in the market this week.
Hence the dump is not far from reach, if you did the basics correctly.
KEYWORD IS: Always do your trading findings diligently.