It looks most likely that a whale is either attempting to manipulate the market with a sell wall or just offloading a significant amount of coins. The chart wouldn't be justified by normal market activity.
I believe that BTC is somewhat overvalued so I won't be buying the dip, but if that kind of price movement happened a bit lower down I would certainly be buying it rather than selling. It doesn't reflect an actual change in market sentiment.
This is bitcoin and crashes like that may occur you can never stop it, but there is a possibility that there is something or someone behind this kind of crashes, if it is from the big whales they surely sell a lot of their bitcoin to make this happen, but if it is from a lot of users this is in an effort of selling out of fear, because big whales don't worry much if the price would go down in a small inch, I think they had a plan in doing this.