I have admit that I would 'normally' just declare PAN PAN in such an event. I add a rider to that, in that in some parts of the world, the PAN call is not readily recognised, in which case a MAYDAY call would be more appropriate.
I think that a basic incapacitation however, does not put the aircraft into a situation where 'the survival of all on board is in imminent risk' (ie MAYDAY), but more into a situation where 'there is no immediate risk' (ie PAN) but where ATC need to put in place measures to ensure priority handling.