The subject is just a person. The makeup and clothing choice was geared toward a seclusionary factor - meaning a result of the conflict. The facial expressions and colors are meant to show the contrast between the two phases. Not that they're opposite, but that they are not the same. My point in showing angst is to connect with the viewer to evoke the emotion - that push and pull of the two sides.
You seem to have a better understanding than the image gives you credit. There really is a clear "opposition" quality here, and if you were trying to go for the "not opposite but not the same" I am not sure it really works, and strongly comes off as a cliche instead.
This aspect though is a really hard thing to explain, because really mania and depression are not at all on the spectrum of emotions. I'd never confuse mania for elation, nor depression for sadness. At the same time, I can clearly see a opposite sort of quality to sadness and happiness, the same is not entirely true of mania and depression. It's like they are two sides of the same coin, both are 'familiar' to one another, but not to the rest of the gamut of emotions that I share with others.
It's hard enough to describe for me.
I very much don't get the seclusion from this image. It's too tight and too aggressively posed; the model clearly is interacting with the audience. I think I know what you're talking about, but I think it's more of an isolation or feeling misplaced. This is frequently described as a feeling of being "wired differently" to others,. I certainly understand this. It's not that I don't understand people as you might expect from autism spectrum, in fact, I often find people predictable and dull - especially so when I am not in remission. Again, it's hard to explain, but I really don't get that (or anything near it) from this image.
From my own experience, I don't feel a "push and pull", it's more like a wave. I don't feel like a leaf being tossed around in an emotional whirlwind and the transition is more subtle than the stereotypical mood swings of a teenager. Symptoms intertwine, it's more of an ebb and flow than a sudden jerk. I am unsure if this is what others experience, but the starkness in your image seems inappropriate to mine and is why it doesn't "click" with me. Naturally others might differ - especially of so-called "rapid cyclers" - which in my opinion, I don't really think exist, at least not as a result of bipolar neurology ... but that's a topic for another forum.
But just as I said of your photograph, we can only relate what we know. I don't mean to speak for the entire bipolar experience, and I apologize if I come across that way.
Regardless, I hope this helps...