I totally agree. When I'm tired it's so much easier to feel overwhelmed by all the little things that you might otherwise be able to put aside. I start to feel hopeless and that everything sucks. When I get enough sleep, I'm usually a pretty optimistic person, so when I start to feel like my sense of humor is gone for good, I have to remind myself that my mood turns around with a good night of sleep. (And with a 3 month old, that usually means 8 hours in bed with about 6 1/2 hours of actually sleeping). So, how to tell the difference between sleep deprivation blues and clinical depression? I think the standard is that you have to feel substantially depressed (not enjoying the things you usually enjoy, appetite changes, irritability, sadness, etc.) for two weeks straight before you should consider clinical depression. If you're worried about real depression you should see a doctor, but probably the real problem is how to get more sleep. Good luck!