Do you choose to hold or sell? I choose to continue holding.
If Bitcoin falls 20% so obviously I will buy some coin. I like to hold Bitcoin. I think Bitcoin will hit $10000 at the end of this year. Then I will sell some coin and I will wait for the next dump.
And that's not only you, a lot of people would do it like that. Tho, depending for what reason did the price fall, we may or may not see the price rapidly going up. Bitcoin these days has a lot more investors and potential investors, so if the price was to go down by 20% as of now, and that's a drop to 6400$ and with that a lot of investors will swarm the exchanges to get BTC that much cheaper, I would do the same as well, but that just might bump the price back up again.