I'm not sure how or why it happens, but based on my nearly nine years of parenting, I've observed that my children always come down with the stomach bug during the night. Apparently, we're not raising daytime vomiters.
Perhaps it's best this way, considering that I react to vomiting with inappropriate nervous laughter and an immediate desire to spray my child with Lysol rather than to hold her hair away from her face as she heaves into the toilet. The cloak of night seems to cover my squeamishness, allowing me to move on autopilot in a haze of semi-delirious grogginess, scrubbing carpets and changing sheets and starting laundry without (much) flinching.
When the stomach bug strikes in the night, the crisis is over by the break of dawn, as if the episode was a bad dream, nothing more, which certainly works for me.
What about you? What's your parenting Kryptonite, the one thing you can't deal with gracefully?