One thing important to mention.
Arbitrage doesn't work in Bitcoin.
E.g - 1 btc = 30 USD = 28.6 EURO
If the USD falls down by 50% - then the Bitcoin won't be valued at 60 USD, yet it will still be valued at 28.6 EURO.
Which means If you sell you Bitcoins for EUROS (which had no change ) and then buy with it USD - you just doubled the your money ( on USD value , of course ).

The reason is that there is no central authority to eliminate the arbitrage difference that is created.
No reason to panic. People aren't stupid - they wont sell it for less than 60 USD.... but only the sellers/buyers will be responsible for doing so.