Depending on the severity of the wound (and I'd say err on the side of caution when it comes to self-harm), going to the hospital is probably a good idea.

As to your first question, I have struggled with it in the past. I started at 11, stopped at 19. From a healthcare professional's standpoint and from personal experience (I'm just a peer counselor), I know that it is literally addictive and very difficult to stop doing. I think I was doing it in mixed states, too. I bake in mixed states now. In overabundance.

I read a really interesting peer-reviewed psych article the other day about the overlap between BP & BPD. It theorized that a LOT of people being treated for one or the other actually had both, and that may be why so many people were what we call "friendly faces" (and the general public probably still calls "frequent fliers" - we don't say that because we're trauma informed and it isn't recovery oriented language). It really resonated with me as someone who both works in the field and has had several family members who were actually dx'd with both. I wish I could find it, but there is really likely a strong link between the two disorders.

Anyway... one of the things that helped me was just doing other things to keep busy until I found something constructive that felt similar... I know that's vague and probably none too helpful, but that's what I did. Help would've been a better route, I think, but I don't handle help well. I also had a child around that age, which was a big part of what helped.

One thing with baking is that you can really beat the s out of that bread... like just pound it. That feels great. Meat cutters have told me the same about their jobs, but IDK with the knives... I wouldn't have been able to do it, which is part of the reason I didn't. But the kneading, pounding, etc... nice release & very relaxing. I managed to perfect a cookie recipe, too, but that was a side endeavor... I mostly baked bread. Now, it's usually cookies.