decompensated phoria - if that, is something that I just live with forever, and maybe it will go away, maybe it will worsen needing stronger prism?
It is unlikely to go away. It may increase and you may need a new prescription periodically.
Similarly, if it is cranial nerve 6 palsy, it may go away when stress and any hypertension lessens?
A cranial nerve 6 palsy improves as the nerve regenerates and regain function. It is important to control the hypertension, but the healing happens on its own.
Which makes more sense if this has really been more gradual than a sudden onset, and was more like over months from start to now. It could explain those times I felt "off, or out of sorts" a few months ago because I was unknowingly struggling with the diplopia where maybe brain could overlay sometimes, and sometimes it couldn't.
From what you have described, decompensated phoria is more likely because it has been more gradual. The double vision with CN6 palsy is generally abrupt in onset.