I have a huge problem with this and have never admitted it either. There is never a day goes by where I do not do this. I find it is the worst in the evening and when I am trying to get to sleep. When I am 'ruminating' I do it constantly. This makes a very big difference to what I wear because of scarring. Arms are very bad. It started when I was kid due to the anxiety from my parents bullying, being very controlling and domineering and my father hitting me - a lot. I find my nervous system is in overdrive all the time. I wonder if I was always like this, or whether childhood experiences changed my wiring somehow.