My Calendar in iCloud erased itself

I recently updated to iOS5. I keep my Calendar on my phone, and everything was working fine. I was able to add items to my calendar on my iphone, and I could view the calendar from iCloud.com.

This morning, I noticed that the calendar on iCloud.com was empty. So was my phone. I think that my phone calendar may have set itself back to PC Calendar by default (instead of iCloud calendar). PC calendar was empty, and when it synced to iCloud, iCloud became empty too. Does this make sense? Any way to restore this?