Holiday Insurance Spain
You will be able to use the Galican medical and hospital facilities if you are an EU citizen, but (in the UK) you will need a form from the Post Office (called something like an E111!) to do so.
Even so, as with non EU citizens, everyone is best advised to take out travel insurance to cover return to your home country in the event of illness etc. You may be surprised at the savings that you can make if you book your travel insurance to Spain with an online travel insurance specialist. Most of these companies allow you to enter details in to a few boxes and get a quote within seconds - they make a good alternative to the general insurance brokers and providers. Also. check and make sure that this kind of cover is not already included in your home insurance.