you shouldn't really wait for such a big drop to sell. if you truly believe in the future of bitcoin and prices over $1000 or whatever you have in mind then it is true but other than that you should sell before that.
i am not talking about a panic sell whenever you see a $20 decline or even the bigger dumps like the bitfinex hack, but instead having a more clear plan.
The main issue with people is they get panic when they see major price drop and start selling their coins and big whales take an advantage by buying at lower price, the best thing is to have patience and wait for the price rise.