I guess to determine if I'm in a "normal mood" I look for warning signs of manic or depressive symptoms and also take situational factors into account.

Like if I'm feeling really stressed and anxious and having difficulty sleeping because I have a big meeting coming up at work, I don't think that's an abnormal mood.

However if I'm having feelings of dread and paranoia during what should be a non-stressful situation (such as going out to dinner with a friend) that would be abnormal and cause for concern.