Are you sure it was a mayday though?
If a pilot has become incapacitated, then the crew complement has been reduced below the legal minimum (assuming no heavy carried), in which case an emergency should be declared.
The first item on the QRH for incapacitation on our fleet is:
"An emergency MUST be declared"
If my FO keeled over on the flight deck, I certainly wouldn't be faffing around with a PAN call.