I think the difference between a generally content person and what JJCM is describing is this:

- A generally content person responds fluidly and naturally to negative events as expected and usually goes back to being happy after the negative event

- If you fall on the mania/Euphoria spectrum, things that should upset you and that do upset others do not upset you, there is literally a natural resistance to changing mood

I fall somewhere between a generally content person and the euphoric, probably closer to generally content - but my resistance to mood change is definitely abnormal in that no one I interact with at work or in my family is as even and naturally resistant to mood change as I am.