If i have 200% gain over night probably i am going to secure my investment which is 100% sell it so that anything happens to the coin you wont lose anything because you got your initial investment.If theres no strong fundamentals with that coin surely it is a PND and you could lose everything if you wont secure your investment on the other hand if the coin which has gain 200% overnight has fundamentals you should hold it until the you are satisifed with your gains.Do not let your greediness eat your chances of getting profits,always secure while you can because the market has high volatility!