Now this won't come as a surprise to anyone out there, but yes, it's true, dark chocolate has a natural pain relieving effect.
Apart from the obvious feelgood effect of sugar which often comes as part of the package when you eat dark chocolate, it's the phenylethylamine (PEA) in the cocoa beans that is the reason for this. Also known as the bliss chemical, PEA is otherwise released by the brain when people fall in love and stimulates release of those feel-good endorphins. Dark chocolate also contains magnesium which can ease aches and pains because it helps muscles to relax.
Apparently cocoa also has good preventive effect on migraines by stimulating anti-inflammatory proteins in the brain, eases emotional stress, and reduces risk of heart disease.
But of course this effect won't come by eating the low grade chocolate you get at your regular convenience store, which has hardly seen a cocoa bean on it's way to the candy shelf. You need the kind that has 70% + cocoa solids in order to get the beneficial effects.
My favourite kind Divine is organic and fairly traded, and I buy it at the local health food store.
Enjoy in small amounts of course :)