So sorry to hear about your arrhythmia, pliepla. I hope it is mild and not severe.
Do you have a psychologist with whom you feel safe and can talk freely? That might help you more than a psychiatrist.
I've hit myself in the past, not so long ago actually, and so your story resonated with me on that level. I take medication, but I don't think it helps with the hitting I think, in my case, I cannot or am prevented from expressing myself... I think I'm overwhelmed with emotion and I do it as a release. I am still trying to figure out the dynamic, to be honest.
Do you have any insight as to why you do it? I'd be interested to hear what you have to say...