I think you reacted appropriately for a parent, and I'm super happy the little guy is okay. I was in a similar situation this winter, staffing a shelter for families who lost their homes in an apartment fire. 6 month old baby, mother, no English, mother begins to get frantic, another client (a 10 year old) translates he is acting very sluggish. All the kids in the shelter have the same cold. We run the shelter, we have no medical expertise to apply here, we treat as per the mother's distress - we call 911. I go out to the end of the parking lot to wave down the Medic One with my flashlight (with included red light filter...) I hear sirens, but they stop somewhere a couple blocks away. After a few minutes, two fire fighters come over the hill on foot, on the run, carrying 30 lbs of gear. Their rig was stopped on another call 2 blocks over, they got our call right after, and they split off and hoofed it as fast as they could to get to us. Man, did I feel proud of those guys - literally coming on the run to help a child, who ended up being okay (but they transported him anyway).

Basically kids can change so quickly as you have seen, it doesn't hurt to 'over-react' for fever, or a bump on the head, or a knock to the mid-section (bleeding). Better safe than sorry.