...Usually, as seen by past trends, there is a major correction in the price of bitcoin when the alts explode. When that correction happens, do the prices of the alts also fall before shooting up?
If the trend says BTC is about to go up, traders will move out of altcoins.
If the trend says BTC is "exhausted" and will take a little break [sideways], traders will move to altcoins since it usually follows after BTC.
It is not always the case but that's the usual behavior that I can see since BTC went past $20K.