As far as I remember, there are wood battens behind the mirror, that the mirror screws to. Mine was not screwed to the wall. I know others have removed their mirror more recently than me (and coincidentally I was chatting to one just this morning!) so maybe they can confirm or otherwise, what my poor memory is telling me?
That’s not to say that yours is NOT glued to the wall, but I suspect that it may have accidentally become slightly adhered to the battens/wall, because of perhaps heat in the substrate, resin in the battens or whatever. Maybe gentle twisting/rotating movements might persuade it free, rather than pulling/bending which will surely break it?
I would hold on for a while, though, and see what other owners have to say.
Good luck.
Barry