bedroom; sleeping quarters
Often implies a married couple's bedroom; somewhat literary or old-fashioned. In modern casual speech, 寝室 (しんしつ) is more common.
The couple returned to their bedroom.
In old Japanese houses, the sleeping quarters were located in the back.
inner room; back room
Refers to a room located deep inside a house, away from the entrance. This usage is rare and mostly found in descriptions of traditional architecture.
寝屋 can also refer to the innermost room of a house.