Have some doubt on it,
When Bitcoin rises, other coins fall because people are selling their altcoins to go into Bitcoin?
It standardized that when the Bitcoin market pump in price most altcoins experience dump in price and as you said people are selling the altcoin for Bitcoin which is what always transpires in the first phase of the bullish market but some people will be worry which is what you are doing now and this is the right time to accumulate some good decentralized altcoin.