I've been in an ambulance twice, both times for passing out (although there have been other times).
The first time was when I was seventeen and I was riding my bike. I have a friend who lives in another section of the neighborhood, but they're only one street over from me. But the weird thing is, even when I had barely started riding my bike, I was already beginning to feel very dizzy- by the end of my courtyard. I wasn't sick and it wasn't that hot out. Well, by the time I had gotten to my friend's house, I could hardly see from blacking out so much, my ears were ringing very loudly, and I kept feeling like my head was basically going to fall off of me. Well, turns out, my friend wasn't home. So I sat on their porch for a few minutes to rest a bit and then started heading home. I made it about halfway between his street and mine before passing out in some grass by the sidewalk. (Since I was riding my bike so slowly by that point, I didn't get hurt.) One of the people in my friend's section found me when I was barely awake. He called the ambulance and took my bike back to my house for me. This was my second time going to the hospital for a medical reason (The first time was due to an extreme reaction to fireants when I was one and a half.). At the hospital, everyone was very nice to me. I got an exquisite plate of food for my troubles and I had an IV, which totally hurt since they kept missing my vain. I stayed until early that evening in the ER.
The second time was not too long after I turned eighteen. I was walking around the neighborhood in the snow when I got dizzy and passed out for, I believe, a few hours. Once again, I was barely awake when someone was nice enough to take me to their house. They gave me food and got me warmed up before calling an ambulance. Once I got to the hospital, they immediately checked to see if I had frostbite since I was still quite frozen. Luckily I didn't. Not really too much happened while I was there this time since it was very, very busy. I went home late that evening.
I have passed out more than those two times, but those were the only times I had ever been to the ER for doing so.