well of course they are going react seriously when they find someone on the floor like that - you seem to pretty cool and collected - hopefully the MRI shows all is well
When stuff like this goes down, I go into command mode and park my emotions. I've always been like that.
Since the ER isn't showing overt signs of concern, I'm going to take that assessment over the words of the facility that is in CYA mode. Time will tell where it goes and there is nothing more I can do except monitor and maintain perspective. The Hospital is one of the best and they know what they are doing. I will elevate my level of concern when I perceive that they are.