Lost All Files in a folder because of undo on my mac

What just happened? I have a flash drive of mine with a lot of school files that I just planned on doing a format. So before I went to Disk Utility then erasing it to the format I wanted, First I backed-up all its files by creating a new folder on my desktop then just copy pasted all my files from the flash drive to this new folder I just created. Afterwards, I went on erasing my flash drive therefore losing all it's files but It's okay cause I did a backup anyways. Now when I was just about to put the the files from the new folder to the newly formatted flash drive, I was about to select all by doing shortcut command "command + a" I accidentally pressed "command + z" instead doing an undo and all the files were lost! After that, finder doesn't even allow me to do a redo! Please help those are a lot of important files now they're all gone in just 1 second and they're not even in the trash. I did a spotlight search of some files I can remember but I still can't find one!