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 
I think now the price of Altcoins in most ICOS is reduced after you buy them. So you should sell them early to avoid more losses. Then you can buy them at a cheaper price if you really believe that it is a good project and can increase prices in the future.