A long time ago I had an accident which smashed my helmet to bits (first time I ever wore one). When the cops and emt's arrived I was conscious, but couldn't answer any questions, even though in my head I knew the answers, but I just couldn't say it. Fortunately the cops knew me (wife worked for pd), and the emt lived across the street from me (emt had a key). They searched my house and found my phone book and called everyone in my wife's family till they found her. Had I been a stranger to them I would have just been a john doe until my head cleared a couple of hours later. Some kind of emergency card is a good idea.