How can you tell if an electrical shock is coming from your drill?

I was standing a metal ladder on my enclosed porch, but the electrical outlet is inside the home, not out on the porch. I successfully drilled the first hole in the concrete ceiling with no effect. The second time is when I felt a slight electrical shock, wearing rubber soled shoes, I should add here, that is was raining outside, but I nor the cord were getting wet or standing in any water.. Any other suggestions would be greatly appreciated. Thanks