Can a health insurance company deny emergency medical coverage based on the final diagnosis?

I went to the emergency room for symptoms suggesting a life-threatening illness. It turned out I did not have a life-threatening illness and the ER doctor diagnosed something much less severe. However, now my health insurance company is refusing to pay for the emergency room fee based on that diagnosis. This seems unethical to me. My symptoms indicated an emergency, so I went to the hospital. Just because it turned out I didn't actually have a condition requiring emergency medical attention, doesn't mean my health insurance company has the right to deny me coverage.
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Most state insurance laws use "prudent layperson" criteria. Meaning...if a "prudent layperson" (i.e. - a reasonable ordinary citizen) would consider the circumstances as an emergency, then the insurance company should process the claim as an emergency. By the way...hospital claims specify the diagnosis you presented to the ER with, in addition to your final diagnosis. So, the insurance company should be aware of the symptoms you presented to the ER with, in addition to your final diagnosis. Its hard to say what happened in your situation, without knowing what symptoms you had that made you feel like it was an emergency. But you should at least be able to appeal with an explanation of why you felt it was necessary to seek emergency care. But insurance companies can have tiered benefits ("emergency" use of the ER, and "non-emergency" use of the ER...based on whether or not a reasonable person would consider your situation an emergency). You can either have a reduced benefit for non-emergency situations, or no benefit at all.
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