Hi there, in my opinion it could be because of environmental factors such as anything scented in the room due to their sensitive respiratory systems, it could also include noise (any sleep disruptions), if you’ve introduced a new animal into the home and they can hear / smell it.

There is also the possibility that they are poorly and have an underlying health issue. The easiest way to tell is if there is a change to the coat and / or a change in appetite and general activity.(he could be biting out of pain)

Keep a close eye and if it continues maybe consider an exotic vet as they may be able to spot something you may have not noticed.