the first thing you have to do is stay calm! don't panic!
now, which alts do you own? are they serious projects or just fraudulent projects who promise outstanding returns??
if you own serious alts don't worry continue to hold! if you own not serious alts sell it and buy something serious now!
after this blood bath only good project will come out alive.
again: you have to stay always calm when this things happen, otherwise you screwed!!