Mac Pro loses disk availability while it sleeps

Yesterday my 2TB Mac Pro disk had more than half of its space available. Today it has only 8GB. What could have happened while it slept? My "User" fold claims to contain 400GB for 28K items, but I can't find any of those items anyway, i.e., all the folders are empty or nearly so since I've moved as much as possible to iCloud. Whatever those 28K items are, they weren't there yesterday but are back today, and I can't find them. ???