Problem:

First off, I don't know if this is a normal healthy thing to occur. There have been many times where I have an itch on say my arm and I scratch it, only to feel the scratching elsewhere on my body. I assume somewhere along the transit of the touch signals to my brain the signal gets mixed up and is processed incorrectly.

Required:

Question 1: Why does this mixup happen? (chemical imbalance, damaged nerves, etc..)
Question 2: How does my brain correspond the touch to somewhere else? (what is the process behind it)