Probably yawning

I have used coco fiber the last 4 or 5 months and haven't had any issues with dust what so ever. As for the hide thing and not being very active...well you probably have a perfectly normal BP. Mine only gets active a few days before feeding time. If you have fed him recently, 2 or 3 days of hiding in his hut is usually normal. Usualy when my guy sheds I wont see him for a week.