This is the main reason they said market is volatile and anything can happen at any given point but how do you control it as an investors or trader, is to have it parted after securing your profit for the maintime. What i mean is that if you buy a coin worth of 300$ and immediately in pump to 500$ first you sell your of 300$ and take profits leaving your 200$ gambling with. Then if you just buy and market declining what to do is don't panic keep accumulating more and  more then you would see that when the market bounces back then you have double of what you had invested earlier.