Does fast licking of clitoris feel good or painful?

I love eating my girlfriend's pussy & I always use my tongue to play with her clits. After a few minutes of slow licking, I always end it with a frenzied licking of her clits, which she seems to enjoy but stops me after a while from continuing. When that happens she will bring her legs together and curl up. She tells me it feels good, but I just wanted to ask if others experience the same & it wasn't painful.