I, too, suffer from Bitchy Resting Face.
Not that I'm complaining. It's a solid benefit when working the ER amongst the drunks and creepers.
One day I woke up and realized I'm not a baby nurse anymore. I'm not even a young nurse. I'm a real adult who has now been doing this for years, and I'm definitely expected to know what I'm doing at all times. And that's fucking terrifying.