Dillon's Psych Appointment

Hey all. Hope everyone is doing okay. I have an appointment set up for my four year old for intake into a psychiatrist. As some of you may know, Dillon is autistic. His tantrums are getting worse. He bangs his head on anything, slaps himself in the face and head, bites, kicks and slaps us. I also believe he is ADD/ADHD as he never stops. Am I doing the right thing? I don't care about him hurting me which he has done before, but I worry about him giving himself a head injury or summat because he really goes at it. Violently. Has anybody else experienced this with a child? Thanks for your support and input. Have a wonderful day.