If you wonder why $BTC suddenly dropped. It started dropping at 09:30 AM Eastern Time (New York).
Guess what happens at that exactly time? Stock market trading opens and it went red. If you compare nasdaq drop is literally the same btc did.
In other words Stock Market drags down $BTC down the same way btc drags down altcoins. As soon as the trading day in Wall Street stops it will be off for the weekend that will give BTC time to recover