Holding is very risky because you didn't know if the price of the coin you hold will return to it's ATH so, be smart and always take the risk. I think it's better if you hold the 50% and sell the another 50% to save even a little if your holding turn to lose.
I agree, hodling atleast 50% of what you have and sell the other half. You'll never know when will its' ATH will reach those numbers again, and as expected, in few more weeks, bitcoin's value may surpass the ATH of 2017. Lets all hope for the best! Lets hodl up to Q1 of 2021.
As long as you hold bitcoin, you should not worry because even if the bitcoin price is down, the price will be back to the higher price. We already saw when the bitcoin price was down deeper to $3k a few months ago, but then the price can rise in a short time, and still increase until now. And we already saw the price can break $10k, which we are waiting for so long. The price will be back to $18k again because the price gets a green candle again, and hopefully, the price will break $18,500 and go to $19k.