Detail of the sleeping area. To clarify in this shot the main,fixed double bed is in lounging set up. When sleeping you have your head at this end and feet go under the back bunk. Storage under the steps.
When a “bird’s nest” of thread appears, the likely culprit is your upper thread tension. If loops appear on the underside of the fabric, the upper thread tension may be too loose. If knots appear on top of the fabric, the upper tension may be too tight.