I think that a lot of people aren't open about feelings of depression. Society in general has the attitude of "If you think positive, you'll be happy" which completely invalidates anyone dealing with depression - it's like we are being told that we should be able to just get over it. So a lot of people then keep these feelings to ourselves so that we don't appear to just be complainers. No one wants to feel like they're being judged, especially when it would just add to the depression that we're already feeling.

It's also a lot easier to pretend than to explain to people we care about that we're feeling that depressed and miserable.

I tend to not fully answer questions. If someone asks me "how are you" I tend to respond by letting them know about my health, or my sleep, or my energy. "I'm pretty busy! It's nuts that XYZ". It's a true statement, just doesn't explain my emotions at all. Or "I slept last night! Was really excited that I slept a solid 8 hours!" or "I've got NO energy today! I'd rather still be in bed!".