A childhood belief about mirrors

I still have not shaken this belief, but when I was little, as long as I remember, I was always afraid that my reflection was not really a reflection, but some "evil twin" in another world who was always looking for the opportunity to snatch me and kill me. I would always be afraid to look in the mirror and be afraid that the other me in the mirror would not be doing what I was doing, and that I would have a heart attack from fear.