Steve, sunshine will help your aches and pains
Stress levels? That all depends on how you adjust to the Philippine culture. Do not expect them to adapt to yours as it wont happen.
Not sure of the statistics but i would say 75% of foreigners retiring here leave at some point. Usually it is not due to one particular incident just a lot of little things really start to annoy them and eventually they cant handle it any more. Your neighbor might decide to burn a pile of leaves/plastic just when you have hung your washing outside. What do you do? Me i just laugh and carry on with my daily routine.
Not trying to put you off mate!