[Blissey]

This is still happening in v.2.19b. A thing to note is that when I edit a specific staff member's clearance level, and then edit it again, it is defaulted to '1'. Maybe that's causing this?

I replicated this with the steps above. Even as Medical Head, I still can't treat Emergency patients. I get the same error.

Edit:
Even as Medical Head, removing yourself from the staff list if you added yourself originally strips your clearance for Simple Patients as well. Re-adding yourself fixes this, but only for Simple Treatments. If I set Simple Treatments to a level above 1, it gives me the same error as Emergency patients.

So I think it's just staff clearance levels defaulting to '1'.