To decide whether you should hold or sell, you need to consider a few things:

Market Trend – Is the overall market going up or down? If the market is bullish, it might be better to hold, otherwise selling may be safer.

Stock or Coin Chart – Is there any support level from which it can bounce back, or is it continuously going down?

Volume and News – Did the sudden drop happen due to news or major selling? If there is negative news, there is a likelihood of further decline.

Your Investment Planning – Do you need money quickly, or can you wait a bit? If your goal is short-term profit, selling might be better, and if the vision is long-term, holding is also an option.

If you provide more details about which stock or coin you bought, at what price, and if there is any specific news regarding it in the market, I can provide a better analysis.