Files have disappeared overnight - where are they?
Assuming the files are actually gone there are two potential solutions I can think of, neither of which necessarily rely on Terminal (which will allow you to see invisible files, but not deleted files).  The first of which requires that you are using Time Machine.  If Time Machine was connected to your backup drive yesterday after you imported your files, it would create a new backup every hour including any files that were new to the system since the previous backup.  Simply open Time Machine, navigate to the folder where your files were previously, and go back to a time when they were still there.  Highlight the file(s) and click the Recover button.

The second solution requires third party software.  When files are "deleted" they are usually only removed from the "catalog" or "index" of the file system.  This means according to the index the space where file X used to take up is now empty and available to be overwritten at any point in the future when it needs to save new files.  Data recovery software simply ignores this index and scans the actual blocks of space on the drive to see if there is any data there. I don't endorse any data recovery software in particular however, as its been years since I've used any.  Searching the web will find various titles, both commercial and open source, and you'll likely need an external HDD to recover found files onto.  Best of luck.