I don't know what qualifies for DBT. For myself I think it depends on the intent behind it or the emotion behind it. Did you mean to hurt yourself when you banged your head? Even though it didn't hurt, did you do it with the intent to hurt yourself and make yourself feel better. If so that is probably SH. I don't think there has to be a bruise or there has to be a break in the skin. I don't think pinching yourself to stay awake is SH but that is just IMHO.