I smacked my head/helmet hard enough that when I came round I heard what in my confused state I thought were angels singing, and remember thinking I wished they would stop so I could hear what the people were saying to me!
I was still sent home once the broken elbow was attended to though, was only there a few hours, most of which was in the waiting room. They didn't seem bothered as I didn't even have a headache (which is miraculous for me, as I get them regularly at the slightest hint of stress).