I've been a self harmer for around 8 years. Recently I've started having dreams about my friends doing it too.. Last night I can remember one in particular; my friend Sara and I were in a block of flats and a guy threatened us with a knife and a brick, one of us said "you can do anything to me, I'll probably enjoy it" and Sara lifted her sleeve up to scars, cuts and bruises identical to mine but when I lifted mine, they weren't mine at all. I really want to know what this means if somebody could give me an insight that would be great! I'm really worried because I've been having these dreams for a little while now. Thanks in advance.

No one can tell someone else what that other person's dreams mean. So such thing.
Only you can decide what, if anything, about your life might have some bearing on the dream.
Dreams are usually a jumble of events so mixed up that new events are created. Whether they serve any purpose other than to use that part of you brain while you sleep is anyone's guess.
So... what does it mean to you?
Perhaps you are feeling isolated and cut off from friends who don't hurt themselves and are worried about losing them, and wish they would join you?

You need to seek help for yourself harming. Perhaps this is a message that you need to ask for help, feeling the pain of not being able to help others

Yeah, I don't have other friends that I know of that do self harm and I've always wanted to have someone to talk to about it without feeling anxious but I would never wish it upon any enemy let alone friends. Thank you.