I hear you

I've also been thinking like this "either I have a mental disorder or I'm a freak". A diagnosis made me feel less of a freak but maybe because I felt like I am "not alone".
Then I realised that I'm still a freak for the "mainstream"

Maybe it's no relevant in your case what I've written here, but still, you're not alone here

And yeah, apparently highs and lows are not considered the "norm", sensitive people with changing moods are still considered weird. I can't imagine myself wanting to be always in the neutral though (I tried to be zen-like but still depends on personality). But sudden mood changes can be a sign of some issues too, depends...