welcome...I dont know about scotland (your profile location) but here in america this out of body feeling due to self injury is pretty common but not called dissociation here. its a definition thing here that changed in 2013.

maybe if you understood about self injury more it would help you.... here where I am when a person self injures their brain makes their body make a chemical reaction called endorphins, this makes a person feel spaced out, numb, extra calm, and not emotional.

maybe thats whats behind this and how to control feeling like this.

example when I would self injure it was to be able to leave behind the stress and problems and get that feeling of calmness, numbness, no emotion kind os spaced out feeling.

but with therapy and special things like learning grounding, relaxation I learned I could feel calm with out the self injuring.

these are the same things that people who dissociate use in order to stay grounded/ not dissociating.

maybe you can contact your medical doctor or your mental health treatment provider who can help you to learn these and other grounding techniques that will help you to not self injure and in turn not feel what your location calls dissociation.