Has anybody here thought to read the docs?
A quick browse of AIP and the CARs reveals:
MED1/2 is
not restricted to RFDS: MED1 is for transporting a sicky or proceeding to pick up a sicky, MED2 is returning medical people after transporting a sicky.
9.2.2 The pilot also retains the option of initiating the communication using the urgency call “PAN-PAN” 3
times to alert all listening parties of a special handling condition which will receive ATC priority for
issuance of a clearance or assistance.
The above paragraph is indeed in the Australian AIP under the title
Weather Diversions so doesn't relate to this situation.
PAN should only be declared when there is a threat to the safety of a flight, ship or person on board or in sight of the aircraft (no mention of medical contidions... unless their condition threatened the aircraft e.g. instantaneous combustion)
Mercy flights are for flights where life is at risk and compliance with regulations is not possible. Where compliance is not a problem, aircraft should declare
SAR/HOSP/FFR/MED - these aircraft will be afforded priority by ATC.
HOSP (Hospital aircraft) is a for international aircraft where carrying an ill passenger.
I think the docs are your friend
As to what response you'd get from an international by saying 'are you declaring yourself a hospital aircraft?', well I have no idea.