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 
Just a friendly tip for you my friend base on my experience if you don't know where would you put your money after you sell you bags of altcoin it will be hard and disappointing. If your planning for a buy back check your risk reward ratio if you can do possible gains in buying back but if you will sell in this current market. the markets is starting to squeeze in it will be hard in your part
because you will always check the price
Future Tip my friend we always have a market cycle kindly anticipate and your problem most probably be solved