I used to have the same nightmare for several years after I graduated about going to the student center(circa 1992) but not being able to find my mailbox. Pretty sure it had to do with the fact that I don’t remember getting anything from my mailbox for at least the last 2 years at Tech. Not sure how I got by without ever getting my mail - which used to be important.
I also had a “real” nightmare where I found out I had an overdue book fine from the library keeping me from being able to register. I didn’t recall even checking a book out that quarter. Went to library to find out it was a book I had never heard of. As I was racking my brain to figure out what the hell happened, out of the blue, an older fraternity brother shows up in my room with the missing book. Dude had graduated and I had not seen him in a good while. He reminded me that I let him borrow my student ID to check the book out and he neglected to return it(nice guy!). Took the book up the library and told the clerk that I found it on the shelves and they must have screwed up checking back in. All fines dropped(like $70 worth - a good chunk of change for a poor student then). I was definitely holding my mouth right that day.