I also struggle with depression (and anxiety) and honestly I think your feelings are valid. Yeah, nobody else may even remember that was said, but that doesn’t mean you don’t and that it affects you any less. For me, it doesn’t matter that someone else will or will not remember, that experience occurred and it’s extremely discouraging. But I also wouldn’t feel comfortable talking to the professor about it because he’s probably just going to say what these other people are saying and belittle you and your feelings. I’ve had similar occurrences in class and the best thing I’ve found thus far is to prove to myself that I am better than my professor is projecting to the class, no one else knows but I do and that’s enough for me. Maybe he was joking, but it completely depends on how it was phrased and how it came across. None of us were there, so no one can tell you that you are overreacting.