It's common for schizoids, for example. Personally, I've noticed that it's more likely to happen the more social contact I've had. Generally I feel a disconnect with my reflection and if I need to look in the mirror when getting dressed or doing my hair I just avoid eye contact. .

At work, if I catch my reflection in a shiny bolt or something while I'm working on a bike, I flinch and have to look away, it makes me feel so uncomfortable.

I also get that floating feeling when having to talk to customers, like it's not me and I'm observing someone else from a distance.