In her native Checotah, Okla., she suffered panic attacks in high school, she told WebMD the Magazine, People reported. Christmas shopping "seemed to be my worst nightmare."
That was because "I'm a big personal space person," she said. "You know, if you go to the restroom, you use the stall that's not near anybody. Or if you're in the gym, you go to the treadmill where there's space in between you. And it seemed like in crowded situations like that, people would just completely violate your personal space."
She overcame that problem, but had to deal with its effects again with her success on "American Idol" in 2005.
Now she has a regime for staying in shape, Underwood told WebMD:
-- Working out.
-- Eating healthy.
-- Washing. "I'd rather take preventive measures than get sick and try to battle things off. So I do wash my hands quite a bit," she said.
-- Giving back. "People think, 'I don't have time to volunteer,' but there are little things you can do to make the world better and raise awareness, whatever your passion is," Underwood said.