I agree with you, panic always lead to wrong decision. Keep calm. After that, Look back your coin, if it's a good coin, you should hold or even buy more coins with low price and wait for recovery. You will get a big profit. But if your coin is not good or it has a bad new problem. You should sell immediately. 
If you panic the best thing to do is to get up and get some fresh air do not take any impulsive decisions, you are only going to make a mistake, so you are going to make a bad situation even worst by making and additional mistake, besides most people panic when they see the price of bitcoin going down without understanding that most of the time the price goes back to normal after a few days.