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(Adding triggering icon just in case)
I'll go to sleep and wake up with scratches on my hands and arms. The other day I woke up with scratches on my face. I know I have dreams, but they are scary. I starting to wonder if I have nightmares but don't remember. I always wake up exhausted too.
I have a history of self-harm.

I doubt you are self injuring in your sleep. When your dreaming you are paralyzed so even if you were self injuring in your dreams, you would not be doing so in real life. Also, not to frighten you, but if you live in an older house there is a possibility that your house is haunted and the scratches come from ghosts. Often times, evil spirits will scratch someone in their sleep.

[Crazy Hitch]

I go to sleep and occasionally wake up with scratches on my face.

Personally, in my case, I think it's unrelated to my self harm.

It tends to happen with temperature changes.

My husband has woken me up before because he hears the scratching - and I haven't been dreaming.