Sudden fall of bitcoin price is a normal scenario in bitcoin and it is normal also for us to feel disappointed with our investment,but the best way we can do is to stay calm,do not sell your bitcoin at low price then regret later.
It is important to stay calm and have patience else it would be a panic selling and it would harm the bitcoin price more as crash would happen more and thus as a result investors will have to wait for more time to get their returns or will have to sell in a loss.