I am a BTC holder. Some People said BTC is going down to $1000!! Is it true? So what can i do sell all BTC or hold it anyone know? 
Actually people can only suggest to you what they have experienced, if that person understands about Bitcoin investing.Knowing or not knowing it depends on you responding to the true meaning of Bitcoin, beliefs are sold and held, even if prices go up and down.
You certainly know that the price of Bitcoin is very sensitive in seconds / hours can change, where someone guesses wrong can lose and vice versa guess right can profit.
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ATTENTION: Trading digital assets is a high-risk activity. Digital asset prices are very volatile, where prices can change significantly over time. please use extra consideration in making the decision to buy or sell digital assets. as an investment, or profit seeking. All digital asset trading decisions are independent decisions by users.
So this is all returned to you in your decision, good luck.