I often lose my temper when altcoins drop sharply.
And in general, I sell altscoin at the bottom
Selling while it's red is a bad move. I mostly do that before but now, instead of looking at the market dropping, I drop my phone and go out to relive the stress of seeing my portfolio drop. Recently I have sold half my coins at half of the price it currently is now because of loosing temper and because I thought it will keep droping but I was wrong. It's best to keep coins and hodl them for longterm if you want profit.
If most of the coins are in red, then there must be a very strong fundamental behind that and the best step to take is to first ascertain and analyse the news/event behind it, to effectively evaluate one's options. Just like now, almost all altcoins are down and that's because holding Bitcoin in wait for the November 16th hard fork translates to free money and people are out to grab as much as possible. At that, it should be obvious that the prices of altcoins would rally again soon after the Bitcoin hard fork and selling off now at their low prices would mean a huge mistake.