My goodness. I can't help but agree with the other comments on here. As someone who worked a veterinary nurse (with animals, not people) I still do my best to calm down the friends I've taken to the hospital, knowing that the hospital workers are busy and doing the best they can. You, of all people, should know that you would have to do your part in keeping your friend calm.

From the sounds of it, your friend was being a bigger baby than the roommate I took to the hospital with kidney stones, the best friend with a cracked rib and the one with appendicitis combined, all over what was probably a migraine. If there had been some evidence of trauma or symptoms of something serious, I'm sure they would have taken it more seriously, but a headache and a lot of immaturity isn't going to get you far in the ER. There are a lot of people hurting worse than you.

And one final good point others have made--he should be making the complaint, not you, as you were not the one mistreated.