The following poster produced by the NHS will help you make the best choice if you think you need medical attention:

In the event of a serious medical emergency you should immediately seek help from someone close by and call the Emergency Services by dialing 999 or 911 or 112 (these numbers can work on a mobile even if you don’t have a signal). If a Defib or a Bleed Control Kit is needed the Emergency Operator will give you the code for you to unlock the Defib Cabinet and get one.

To help you in a medical emergency you should identify a number of ICE (In Case of Emergency) telephone numbers on your phone, list your key personal and medical information in a Message in a Bottle in your fridge, and ask a friend or neighbour to be your Personal Buddy who you can call in an emergency to help you until the professionals arrive.