It's possible to be happy but still feel sad or suffer depression

I've just been discovering that the above is not an oxymoron.  At least in my opinion. 

Earlier this week Chel came downstairs feeling a bit 'weepy' all of a sudden for no reason that she knew of.  But she is basically happy these days and is enjoying her happiness.  She doesn't understand the mood stuff.  Nor do I.

I do know that I'm really deep down happy.