If you come from UK/EEC please carry your E111. You will be asked for this if you have to attend a Doctor or Hospital. Treatment is free.
In addition I had travel insurance and I am afraid I had to use it. When I was stricken during the night I was able to telephone the insurance company emergency line and explained my problem to the operator who spoke English and Spanish. He made all the necessary arrangements. The ambulance crew had been told what my problem was, as had the hospital. It really helped when I didn't feel up to struggling with the language. The company even paid for a taxi to return me to the hotel next morning.
My advice is to take out BackPackers insurance in addition to the E111.