No, fainting is fainting, can't know the cause by just looking at them really, unless there are other symptoms present. If someone faints, put a cool cloth on their head (with water is best) and prop their feet up. Not sure what an EMT would do, you don't stay out for longer than about 5 minutes or so, but they'd probably give you a glucose injection.

When I'm about to pass out, or I have passed out - that's what I do, or people do for me and it works well. I lay down with my legs bent at the knees in order to get the blood flowing - and I have a cold cloth on my head and under me on my neck. Also - eating ice chips when you wake up is great. That always makes me feel better.

I assume the person in question would be hypoglycemic (reactive) and not diabetic.

When I pass out it's not for long, I come around in my own time and an ambulance is not needed. When I do come around, the first thing I want is food/a drink. The last thing I want is fussing. Allow the person to sit with their head down (most will automatically take this position), and don't force them to stand or do anything they resist.

If it's reactive hypoglycemia their blood sugars should correct themselves enough to regain consciousness without the need for an ambulance. If they're type 1 diabetic and you don't have necessary glucose, call an ambulance.