50% loss of power.... I've had a few of those as a controller and heard neither Mayday nor PAN calls associated with them. Once during fog an A310 made two go-arounds at Heathrow. On the third he said he had lost an engine and wished to divert to Manchester, which he did. He did not sound in the least bit perturbed!
I've also had a couple of cases of loss of 50% of crew - Captain or F/O incapacitated. Far from screaming into the mic, one F/O simply said: "Be gentle with me, I'm all alone as the Captain has been taken ill".