So I was trying to clean up one of my USB keys that I throw linux distros on to test them out, and did a dd if=/dev/zero of=/dev/sdd. For those that don't know, this zeros EVERYTHING on the drive.
Didn't realize, I had ALSO plugged in my USB drive that I keep ALL my stuff backed up to...and it was plugged in first, which means IT was SDD. So...I get to download EVERYTHING again. I lost about 300 GB of files...
Whoops...