Also, document everything - screenshot the call log, note the exact time and circumstances. You may need this for Apple support or potential legal action later.
Hope you recover quickly.
If you go to the ER, they may be able to start you on a course of prednisone or similar, which helps lessen damage from acoustic trauma if started within 24 hours.
That leaves it achier than before, still ringing, but they said it should self-resolve mostly and I will follow up with ENT after the storm.
I think what I can do to test the earpiece volume in loud env vs quiet is attempt to use an old earpiece microphone (suction cup mic) I have and run the levels directly into a sound card, it won’t give me absolute volume but I can at least compare the levels and see if it warrants further investigation past that.