That's a reason why it's not good to hold altcoins for long cause they can fluctuate and crash so easily, it's more advisable to just engage inshort term holding and take profit and run.
Altcoins are normally short term investment unlike Bitcoin who can withstand both seasons without entirely loosing it's value to nothing. Anyone getting involved with Altcoins should be very careful and good at timing time of entry and when to dismiss from the holdings.