There are two basic things that need to be implemented when the market suddenly falls like yesterday to make a profit. First, the attitude must remain calm by thinking that it will recover. Second, take the opportunity to buy as many coins as possible, such as top 10 coins.
I agree mate, remaining calm is the best way you can do at first especially at situations like this and don't panic when the market falls sharply because chances are you'll make wrong choices.
Don't sell your coins immediately just because the market suffers declination, instead think of it as an advance and buy coins while the market is low in order to have profit when the market recovers. You should plan it carefully what to do when experiencing situations like that ans always have a plan B.