Mental health ramble
I see mood as a three-dimensional thing.
One axis is perspective. Good or bad. This is what people usually mean by "mood"; they're having a good day or a bad day.
Then there's sensitivity. How easily your mood changes based on stimuli. Depression is low sensitivity.
Last is anxiety. How much you're expecting changes in mood.
So you can have a "good day" while being tense and numbed by depression. "Bipolar" is sensitivity bouncing around.
Just a thought.