I think calling a Mayday or Pan ultimately depends on the circumstances, where you are, where you can get to and what assistance you might need etc
I was doing aeros and on pulling vertical heard a change in engine note and felt a slight vibration so headed back to the airfield (a mown patch of grass with a cowshed at one end where the plane lived) I didn't call mayday as I wasn't going to make a proper airfield so no one to help, I wasn't near controlled airspace or 100 miles from anywhere so the only point would have been to dial 121.5 and say 'tell my wife I love her and tell little Jonny to be a good boy'
besides the radio wasn't even on...