I think the suggestion of a basic first aid and cpr course is a good one. Even better would be a Wilderness First Aid or First Responder course. You always have to be careful about trying to do things that you're not really trained/prepared for.
For the most part, you're trying to keep the person alive long enough for the EMS system to kick in and get them to medical care. That means having someone call 911, or the equivalent where you are, and having them stay on the line! Assign someone to keeping the scene safe, so more problems don't arise. For the specific victim, you start with checking the patient for awareness, alertness. (The "ARE YOU OK" yell and shake). They can sometimes tell you what's going on, but, if they're unresponsive, then you start with the ABC's. Airway, Breathing, Circulation. We can't do a CPR course, here, but it would be time well spent for anyone not current.
Sorry that you had to find yourself in such a situation. That had to be a tough experience.
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- Ron