Every traders must learn from their mistake. Just a little percent of them who not do it. Like me 
, i know i always panic. But until now i can't get out from that feel every market get down and i loss my assets.
At least you acknowledge your mistake. It is the first step in correcting which is identifying the topic where you are weak and then you need to work on that in order to improve. To prevent panic from happening invest in those coins that you are confident about in terms of future gains. Remember that every altcoin creator out there is after your precious bitcoins and in no matter what circumstance you fall in the amount that you give to their coins should be minimum and cashed out to bitcoin as soon as you get some gains in price., i know i always panic. But until now i can't get out from that feel every market get down and i loss my assets. These are not to be held for long term rather cash and dash is what should be in your mind.