Based on the current market situation, we should hold our bitcoins and other crypto assets while market is down and wait until it recovers again. If the market is good, selling of bitcoin is depends on you who buy and invested because you are the only one who knows if you already gain profit or not yet. If you are a long term holder, I think you have a very high target value before selling your bitcoin but as a trader you will always  ride on the market movement which is sell at high and buy at lower price in order to accumulate earnings.