The Periapt of Wound Closure's description says
While you wear this pendant, you stabilize whenever you are dying at the start of your turn. In addition, whenever you roll a Hit Die to regain hit points, double the number of hit points it restores.
Emphasis mine.
What happens to a PC wearing Periapt of Wound Closure while suffocating? I'd like to transport myself using a Homunculus and a Bag of Holding, but I worry about suffocating during the journey.
If I put on a Periapt of Wound Closure and enter a Bag of Holding, will I suffocate to death while inside of the bag or will the Periapt keep me alive?