You need to separate your funds between different crypto-currencies and not invest the money that you are afraid of losing.
Bad advice, if you look closely at charts, you may notice that altcoins usually go parallel, they drop together if BTC surges, so if crypto bubble bursts, all cryptocurrencies will drop, and I'd say that altcoins will suffer much harder than Bitcoin.
To OP: if you are afraid of losing, you can either quit now and abandon all potential profits, or you can set a stop-loss order at the price you are comfortable with. But keep in mind that if you put them relatively high (like, -5% of current price), they might get eaten by volatility and you will suffer some loss.