so far as I understand it, the criteria for warranting an ambulance is that some muppet, be it the patient, a family member, or a bystander, decided to call one... and that sometimes people who really should call an ambulance "don't want to be any bother". As for bangs on the head, about ten years ago I had a nasty one at school on concrete, I lost consciousness for about a minute, and the dinner lady plonked me in the receptionists' area for the rest of break on the basis that "it's not bleeding, you'll be fine, just a bit dizzy." If I hadn't thrown up when I tried to get up to go to class, I don't think they'd have even called my mum. She called a doctor for advice, the doctor told her to bring me in to the surgery, he examined me and then called an ambulance, and wrote an angry letter to the school saying that with head injuries it was better safe than sorry.