When I was young, I used to go into modes of crying, silent crying in my closet or bed at night, real gut-wrenching crying that would make me have to throw up, then I would escalate and bang my head, punch, bite, pinch or scratch myself. Only in private would I do these things. I felt that if I could scratch deep enough, I could rip out of my skin and be free. Of course, it didn't work. It wasn't something I did deliberately and regularly. Just overloaded with emotion and not able to deal with it. I haven't done anything like that since I was 11 or 12. Deliberate cutting at unemotional times, I think, sounds more serious and difficult to treat. I would recommend redirection. Make yourself do something constructive, even if it has a little element of danger. The best thing to do would be get help! I don't think that everyone can do this on their own.
A little word of advice: don't watch depressing and dark movies and books. They just deepen the love affair with despair. (and lead to paranoia for some!)
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"Honey, would you buy me some boobles for my 40th b-day?" "No way, they're too expensive. Your own baubles will have to do."