The EU is a single market, and economic policies are governed to some degree by Brussels. I guess it's open to interpretation, but most sources I've seen describe the EU as a single economy, including the CIA world factbook.

They are only economical sovereign within strict limits. Greece might be able to tell you a bit about recently having to implement unpopular economic policies demanded by EU.

And for all of the troubles in California and other states, I'm not sure if any of them required the sort of bailouts that the PIIGS needed.