Of course it's different for everyone (since we all have unique personalities and temperaments beyond having bp), but I wonder this A LOT too, and so far this is what I've come up with:

'normal' high mood = sense of well-being w/o feeling the drive to do a million things (happy just to 'be') and w/o the more physiological signs of hypomania (not buzzing/hyper, normal sleep/appetite). Hypomania = I'M SO GREAT!!!! Happiness = Life is Great!

'normal' low mood = being however upset and sad and crying but still wanting to be alive, maintaining some semblance of perspective, can be distracted/cheered up.