It's quite obvious to see Altcoins' orices dropping as the fork is near and most of them are awaiting for the airdrops of BTG.
Most of the people i know have sold their Altcoins to receive the free coins. That is the main reason why Altcoins have dropped.
The other reason is the increasing price of Bitcoin which has implemented a decline in Alts price making it drop gradually over the few days.
The Altcoins will rise after the fork when people will sell their BTC and invest in Alts. So don't worry and be patient.