Why do I feel like my sensation has lessened?

It seems like my skin is not as sensitive to touch as it used to be. I often engage in self-harm and I am worried that this is the reason for it. Can repeated strikes to the neck or head lead to diminished sense of touch and temperature? Can it be a sign of injury?

I have no trouble maintaining balance. There is no muscle weakness. I do not experience pain or tingling anywhere through my body. I would like to know the reason for why I am feeling this way.