Panic is the most enemy of traders as it makes you to lose money. Professional traders take sell or buy a coin Base on their analysis of the trend and good knowledge of technical and fundamental analysis and event. I will advise traders to study very well before burning they fingers in the name of trading. Like op said all coins get dump time to time.
In every dump ,there's always a pump. It may take time but when it happen it definitely worth it. When we panic that's our lose we might regret it when time comes that we see those coins we sell having position in exchanges ,so better relax,think and never panic unless you need that money in that very moment,secured it then.
Yeah, I'm usually holding my coin no matter what happened on the price, I'm only setting a date for my convertion of all my altcoins no matter what is the price is. So that I will not panic or think anything that might distract me. Being in panic will not gonna help us.