One of the reasons for the drop is just the sheer volume of the market. People who jumped in at 20K Bitcoin seen a 100% profit at 40K and in any market that usually means making and taking a profit. These are mostly the financial institutions who now have such power over the market that they can actually cause it to rise and fall, with all altcoins following and reacting to Bitcoin's fall. 

At this point, there are no indicators that the fall is over and a rebound imminent. Do I need to tell you to hold if you are in the loss column? It will bottom out and eventually it will rise again. What matters is the number of coins you have in your bag and not the value of your bag, unless you are living off crypto, which most people are not and see it as an investment and long-term wealth generation.  

If you are in the red, do not sell your crypto! Do not make the mistake that so many others have made in the past. 

Taking a loss is never acceptable. 

The market will eventually recover. 

Look at it as a buying opportunity, 

Update: Looks like a short or long-term rebound is on the way today 1/11/2021