Nationals of EU countries are eligible for free emergency medical treatment when staying in Spain for less than 90 days and on production of the correct documentation.

If you are a resident of the United Kingdom, you need to obtain form E111 which is free and available at most main post offices.  In addition, it is advisable for holiday makers to arrange private medical insurance to cover for other eventualities.

For those living and working in Spain, you are entitled to free or subsidised medical and dental treatment if:
you pay Spanish social securityyou are a retired EU resident receiving a Spanish state pension
you have paid social security contributions in another EU country for two full years or more prior to coming to Spain, you will then have cover for a limited period.
you are a retired EU  national of retirement age who isn’t in receipt of a pension, but can prove you cannot afford private health insurance.

If you need an ambulance, 061 is the national emergency number in Spain.   Alternatively, taxis by law must transport a medical emergency to hospital if requested.  Should you need to use a private vehicle to transport someone to hospital in an emergency, it is usually sufficient to put on your hazard lights and wave a piece of white material out of the car to gain priority over other vehicles.

If you are able, you can go to the casualty department of a hospital or a 24 hour public health clinic.  If you own a property in Spain you should find out your nearest hospital casualty department and how to get there.

There are also 24 hour private clinics in many areas, and they offer a quick service at all hours, usually at a reasonable price. 

You will find that many chemists post a list of local clinics and hospitals where emergency treatment is available.