>>283597432
Per Furinkan: "The drawers in the background are often used in Eastern medicine to hold various items which are then crushed with a mortar and pestel and then mixed into a powder. These are called "kusuri tansu" (薬箪笥)."

Also, Mao seemed to just say "I slept well". I think VIZ added the bit about him thinking of it as a nap to make it a bit more comical.