Panick sell is the worst thing you can do when price is down.
I think no one can know what is expected for Bitcoin or any other cryptocurrency. Unlike what a lot of people think December was the best thing ever happened to Bitcoin, since then so many developments started for a better technology and for easier UX; with the purposes of mass adoption.
It's really all about DEVELOPMENT, more things need to come and become better and if everything will go right then Bitcoin can reach 1m easily.
Exactly as it is? Bitcoin will die to $0. But the good thing is that it's always getting improved by protocols and third-party developments.
In my opinion the three things not to do when the price are down are 1. Never sell your coins because due to low price you will lose your money. 2. Dont be panic and hold your coins till the price rise again. 3. Build your trust and be optimistic about the future of bitcoin or any other currency in which you have invested. Strongly follow these three things.
Rather than not selling when the price is low, I feel it's more important and necessary not to panic as you said later because you may need to sell and then you may sell. But if the investor panics then even if he/she doesn't need to sell, he/she might sell off his holdings.
I would suggest Not to Panic, Diversify or trade to get some other coins which can provide greater return percentage compared to BTC, Be optimistic even if countries are temporarily banning or restricting usage/trade related to cryptocurrencies. And most important, follow your own strategy, don't follow others.