Say I have a severe allergic reaction, or cardiac event, or poisoning, or any of a billion other conditions that would require urgent medical care, but might leave me unconscious or otherwise unable to provide authorization to release my medical records to healthcare professionals. If I'm not a minor, can my parents authorize said release? Siblings? Spouses? Other family? Friends?
If you are in the US, doctors can access your medical records in an emergency in order to render appropriate care:
The Health Insurance Portability and Accountability Act (HIPAA) Privacy Rule sets rules and limits on who can look at and receive your protected health information, or information that relates to your health or health care you have received and can also be used to identify you. Your health information may be used and shared with doctors and hospitals; with family, relatives, friends, or others you specify; with the police in special cases such as gunshot wounds; and with government agencies that report on the incidence of various illnesses.
But consider that in many cases, if you arrive in an ER unable to speak for yourself and no one to speak for you, they'll have no idea where your medical records can be found. This is why you should carry a medical card, tag, or ICE entry in your cell phone listing any pertinent conditions you have or medications you're taking. For example, things like a seizure disorder, diabetes, heart disease, prescription drugs, or a medication allergy would be important for emergency personnel to know.