You said the arm scratching is something you can't control? Does that mean you do it unconciously?
If so, it's similar to when I sleep, I clench my fists, sometimes so tight my nails make my palms bleed.
Some people grind their teeth without realising (either asleep or awake). One person I knew would sit and move their jaw from side to side and make it 'click' without realising.
It's a nervous thing, not in a 'scared' way.
It's your mind making your body do things to calm itself.
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The wall hitting due to losing an element of self control from all the pent up frustration and anger coming out.
I used to do it.
After all the sh*t kept building and building, wham.
If the arm scratching is due to loss of control when you get p*ssed off (like when you get p*ssed off and hit a wall) then it's a 'release' thing.
You're releasing the pent up cr*p in your system, rather like how you said you have a good cry and it makes you feel better.
I hope my rambling explanation has helped

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I will say again though, you have actually spotted these things you're doing, and you know something's not physically right, which is a good thing.
Most people don't even realise their own physical changes and only concentrate on their mental state, so well done you. Very well done.
In any case, you really should see your Doc.
Don't feel embarrassed or scared, or feel you're letting anyone down or bringing them down.
You're not.
Really, your not.
The Doctor should always be the first port of call for anyone who is in these horrible situations.
Though taking that first step is daunting I know, but the Doc is a doorway to lots of different kinds of help and to people who know exactly how to help you through all the sh*t, both mental and physical.