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 
Could you please determine what altcoins you're holding right now? So that we can help you with your problem. Because if the altcoins that you're holding are including to those shit coins, there's no reason to still holding with all of that. Because it will leads you to lose a lot of your money in the near future.