This happened maybe a month or two ago, but I haven't played Minecraft in sometime, so I forgot about this, until now. 

When logging in to one of my survival worlds, I noticed that my normal skin had changed into one of the default skins, Efe. I haven't changed my skin in quite sometime, so unless I accidentally chose it in the launcher, I'm not sure how I've got it.
I checked my launcher, and it still says that I have got my original, non-Efe skin selected. Any new worlds I create, also has my original skin showing. However, when I checked to see if it's just my survival world that has the Efe skin, it turns out that any pre-existing worlds all show up as the Efe skin, rather than my actual skin.

I'm not sure whether I've missed something about this happening, or whether it's a bug or not, but any help would be appreciated!