I agree with the others who have said it's not necessarily just happiness per se. It's the whole picture, and that picture can look different from person to person. So, the first thing to do would be to make a list of things that tend to happen when you are manic. Do you sleep less? Do you spend money? Do you want a lot of sex? Do you turn to religion? Start lots of projects? Business/education plans? Cooking? Cleaning? Having any hallucinations? etc, etc. Don't focus so much on the happiness level, but focus on what it is that you are doing. That's the real hallmark of mania for many people - we don't usually sit still with our euphoria - we're all over the place and can't stop doing things with it! But mania can also be rageful and angry. That's something to try to notice as well, and should be on your list if you feel it applies to you.

Mood per se can be a tricky thing to gauge, but how much you're sleeping, how much you're spending, or needing sex, or making plans, or, or, or...that's something concrete that can be measured much more easily than whether or not you laughed "too much" that day.