Upvote:0
The worse thing that can happen is having to pay for the treatment yourself, possibly at some inflated/non-regulated price. A slightly less serious problem is having to pay the regular price out of pocket, with a lot of paperwork to recover (some of) the money. I don't think you could be refused treatment for an emergency in the EU countries I know.
Also note that the healthcare systems differ widely between EU countries. What the EHIC offers is a level of coverage similar to the local statutory/public health system. In some countries, it means healthcare is free at the point of delivery or you might have to pay only a small part of the costs out of pocket. This makes any insurance claim after the fact more difficult that in countries where people routinely pay out of pocket.
Upvote:2
Yes you do need one. As someone from the UK who had to use a doctor in Spain, you will be presented with an estimate of charges which you will need to pay by credit or debit card before treatment begins. The initial consult with a GP can cost several hundred pounds before any real treatment happens. I made sure we had EHIC cards as soon as we got home, and always carry them on EU holidays.