Lightning What is lightning? Lightning is a bright flash of electricity produced by a thunderstorm. All thunderstorms produce lightning and are very dangerous. Achilles tendonitis and Achilles tendon pain are common injuries, especially in runners. Learn natural treatments and prevention for Achilles tendon pain and foot pain! A bump on the bottom of the foot can be irritating or cause pain while walking. Many causes of these bumps can be treated at home, but some require medical attention.