I'm sorry. The number one best thing to do if you want the sensation of self harm is to get in the shower and turn it on super cold! It's painful and after you turn it off your body reacts the same way. You can do it a couple times, too.
When I used to do this, I would still have the urge to SI afterwards even though I felt calmer/better, so I would use a red pen/marker on my arms or hold an ice cube against my skin (the face is very grounding). I would also recommend doing any and every grounding mechanism that might work for you if you're committed to not self harming. Hospitals suck and you don't need them just because you have this urge, it's only if your life or someone else's is in danger. Please stay safe