This might sound overly simple, but open a new finder window and put it in list view with Date Modified selected at the top. Then just move through major folders to see what was added. You could also try switching from Date Modfied to Size since this is a big chunk of data obviously. See if that allows you to find where this data came from and you can then compare to your HDD. Again, not super technical, but since there haven't been many responses, I figured I'd throw it out there as an option.
When I quit out of Photoshop, I got all the space back.
When i opened PS back up, a myriad of gigs was missing again. There must be a cache that photoshop was holding.
I tried to "PURGE" from the edit window but it was greyed out. So, I tossed that PS file and started over. All is back again.
That was weird. And scary.
Thanks for the replies