Am I being selfish and is it bad I don’t know why do it??

im doing the wizard of oz with one of my theatre groups and we all were getting changed in the changing room and I saw loads of healed and really fresh scars all down someone’s arm and it made me really feel the urge to self harm and now I can’t stop thinking about it, it’s none of my business though?? But I can’t stop.

I have no reason to self harm or be depressed I don’t know why I do it just feels good and distracts me but I have nothing to be depressed about really?? I mean mg social anxiety and low self esteem really makes me feel crap but I don’t have any trauma or anything like that