How can you end up in the emergency room?

You should go to the emergency room whenever you feel whatever is wrong coudl cause death or permanent injury, or is too painful to endure, until less acute medical services are available. Also, emergency services in the US are required by law to see you if you feel the situation is really an emergency. The billing will come later, but can't be used as a reason to not see you. If you have an emergency and are worried about the bill, this beats not treating an emergency at all.