Optional Rule: Sleeping in Armor
I’m a big fan of trying to make the game as immersive as possible and few things ruin that for me as much as players treating the game like they would a video game. Conventions shouldn’t be the same, instead they should try and describe how their characters live in the world. An easy way to get this across is having npc’s regard the appearance of the players. If they walk into town with their weapons attached to their hips, clad in armor then maybe the villagers fear them a bit. Likewise, it’s unlikely you will find a warrior sleeping in their full plate mail.
To this end, I present an optional rule for DM’s (at least until Wizards releases an official ruling on the matter):
Sleeping in Armor
Any character sleeping in armor (PC or NPC) that is heavier than light has disadvantage until they’ve taken a short rest.