I may have used Disk Utility to erase my drive - is there hope?
Try plugging your drive into different computers (Mac and PC). If you don't see anything, you will probably have to send it to a data recovery service if you don't have a backup.
You can also try software to recover data, like DiskWarrior.

As for why DU erased this when you clicked Repair, I have no idea. Are you sure you didn't click Erase, Reformat, or Repartition?