there is no panic, and the panic that you are talking about is only among newbie traders/investors who have no idea what they are doing with their money. they have thrown their money on bitcoin because someone said it is going to the moon and they will sell when another someone says it is doomed.
if you have a mind of your own, you will never panic and will always make good decisions which will lead to more profit.
What you are missing is this: If a alt coin falls while BTC rises does not automatically result in that alt coin rising when BTC is falling. So after the BTC dump happens some altcoins will be worth significantly less.
The interesting thing is ETH seems unaffected by the swings of BTC as of late when BTC up and all the other alts go down ETH is staying stable
because ETH is premine scamcoin which is being controlled by those who are holding the ~70 million premine coins. and anybody who is controlling that much money will control the price, his assets with all he has!