Okay, maybe the extended trip frightened away the evil spirits. There is no security code for the trunk, nor am I aware of any release mechanism. It could be that somehow a tight seating has developed between the trunk lid and the rubber seals (cold, wet weather), so you might try putting the key in various positions, pushing in on the trunk button, and just giving a mighty heave on the trunk lid. Also, if you have fold-down rear seats, that would let you get into the trunk that way and poke around with the locking mechanism, it doesn't seem like an electrical problem.