On occasion, I've returned from a dive trip, even just long weekend trips, and it seems like everything is "muffled." I don't have trouble hearing, but it's almost as though I have a small piece of cotton in my ears. When I went to the Dr., he told me I had a minor ear infection, prescribed some antibiotics, and the problem went away.
As NurseShark mentioned, this was after diving in those warm Mexican waters. I've been to Coz quite a few times, and the problem has only happened twice, so I guess you never know.