Currently I own a lot of altcoin, I bought them at ico. My account is being downgraded several times. There are many people who say bitcoin will continue to decrease, so altcoin prices also decreased compared to USDT. So now, should I sell them and wait for the price to buy back? Give me advice 
Anyway, it is much better to hold it first if the price is still decreased. You can only help yourself it is your decision if you hold it or sell but as my advice be careful to what you do and think wisely.