Wait for a few members to comment before attempting any HDD fixes.
Your data might get destroyed if the fixes aren't done correctly.
It's possible that the Hidden file attribute was toggled by something.
Try changing the "Show hidden files, folders, or drives" setting
Hidden Files, Folders, and Drives - Show in Windows 10
File Explorer > View Ribbon > Options button > "Change folder and search options" > (Folder Options window > View tab).
Click on picture for animation
Recently I managed to damage the file table on a data drive and Check Disk was able to repair it (mostly).
I only lost a handful of files.
Drive Error Checking in Windows 10