Thinking about it I guess I equate energy levels with mood. What does mood mean to you?
I associate them more with emotions.
"He was in a good mood" = "He's happy and its infectious"
"He was in a bad mood" = "He's angry or depressed etc. and may snap at you, or dismiss you for little cause"
Admittedly what others think of my "moods" may not always be in line with my own opinion. A "bad" mood ( someone pointing it out to others about me ) might just mean I'm working something out that requires concentration, and so I don't want to be distracted by others.
People will rarely acknowledge being in a "bad" mood ( except retroactively ) , and I think this is due to two reasons.
( 1. ) Connotations of the word "bad"
( 2. ) The phenomenon I mentioned earlier, that the very thing which would be observing is affected.
Oddly enough, people will often be surprised if told they "seem to be in a good mood" too, however. They usually won't go so far as to deny it, in this case, though.
It's funny, but I've noticed that whenever children are crying in a family atmosphere, the parent will invariably explain it by saying "S/he's just tired", but sometimes the crying started the instant the baby was told they were going to the bedroom for sleep.

I asked my brother in law to explain this seeming contradiction once, and he said "He's just afraid he's going to be 'missing out' on something that happens while he's asleep."
I wonder how many of us are doing the adult equivalent of this with a "mood" signaling tiredness that we don't wish to acknowledge ?
Yet I believe that I can be angry or depressed without being tired. I am told I am likely an "F", though, and I make no "Mr. Spock" pretension about being objective about myself.