Yeah, maybe that is some sort of depersonalization. I don't have this as a constant state but it's happened to me a few times, the mirror thing you describe. It is creepy. Do you ever have thoughts that seem like they were put there by another person? I know there is a disorder in which it seems like you are not in control of yourself
No, I don't have thought insertion. Though schizophrenia runs in my family (two brothers, aunt, grandfather), and I do sometimes experience things that might be considered borderline psychotic.
I do have intrusive thoughts of violence, though. And those thoughts are associated with physical urges I have to resist acting on. (Like stepping in front of a bus or stabbing someone.) So I often feel like I'm not totally in control of myself. Those moments where I have to fight violent or self-destructive urges are frightening precisely because I'm never sure I will
be able to control them. But I've never acted on them, and so far as I know, that's just OCD.
The mirror thing is creepy. Which is why I try to avoid triggering it. There's such a disconnect between my mental representation of myself and what I see in the mirror that I sometimes feel like the two are unrelated and that I somehow took possession of a body that doesn't belong to me. When you combine that with my OCD urges, what it feels like, sometimes, is that my body is at war with my mind and trying to rebel. It's honestly pretty ****ed up.
But these are just ways of describing subjective feelings and sensations. They're not delusions.