IIN to feel I HAVE to touch one side of my body when I touch the other

I have the EXACT same thing, it's really embarrassing sometimes because if my friend hits my arm or steps on my foot I would have to do it to the other foot or arm, I've even asked as friend to hit my other arm. I'm so used to doing it that it's natural for me to do it I do it automatically. I don't have any idea what it is either.. :L