If you called your PO prior to going to the ER, then yes, you would be okay. But if you totally missed your appointment and did not bother to call while in the ER, then quite possibly your PO can and will violate you. Did you call the PO before or after going to the ER? Do you have paperwork from the ER to prove where you were at what time?
The gist of this is basically you will be violated and then have the luxury of proving where you were. Unless you were unconscious while in the ER, you will be violated. Sorry.
There are extremely few legitimate excuses to miss an appointment with your PO without calling first. Being unconscious is one of them. Being dead is another.