As long as you didn't execute sell there's no REKT or losses in your portfolio. Holding is the best when you saw that the market getting worst because it is still a number of coins but the difference is to have the lowest value compared to dollars.
Panic selling is the most common factor of sudden loss, because of fear, you will blindly accept that you have a REKT, the price will not go beyond zero and that is impossible. The nature of cryptocurrencies is the volatility price and it will obviously fluctuate with or without reason.
Well, many people look at their portfolio and feel "rekt" just because of that. I have a friend who got so scared of what he saw and he was in panic mode, I just told him to stay calm and his money went up again, not to where it was but at least it got up a bit more, and then he was like "oh then I can wait for it to go back up" like it is some marvelous new invention. Basically things are not as simple as it looks in this world, some people are just way too emotional, and that is why we have to just accept them the way they are.
I personally do not sell bitcoin, I have NEVER sold any coin for profit, I did had periods when I needed money urgently for some life emergency so I sold some, but I have never sold it for profit, which means I have been keeping my coins for god knows how many years and I will keep doing that until I have enough money to retire.