Have you checked your eggs? Maybe they've gone rotten? (okay...just kidding).
Have you looked in the outside fridge compartment to see there's anything there that looks like yellowish dust? That could be indicative of a leak. (How unlevelly were you parked?)
And have you checked your battery electrolyte levels? Batteries sometimes smell like rotten eggs if they've boiled due to overcharging (as Biscuit noted).
I'd check those two things, even if the smell is no longer present.
(EDIT: There oughta be a "What's that Smell" subforum. Or at least a sticky.)