At some time after I left to take Katie to the softball game, but before Gretchen and Julie left to follow us, there was apparently a horrible noise somewhere in the house. When I got home, Gretchen mentioned this to me and asked me to look around upstairs. I did and didn't see anything obviously wrong.
Thus, it was not until Gretchen went to hang up the shirts in my closet tonight that the problem was found. The long shelf in my closet had fallen off the wall, making it nearly impossible to open the door.
We have now piled all of my shirts and the contents of the shelf elsewhere. And I need to figure out the best way to fix this, because things are pretty much an unholy mess.