Some people need more personal space, cooler air, or a certain posture to relax. Turning away can therefore be completely normal and may have nothing to do with emotional distance.
In fact, sleeping back-to-back can sometimes show that both partners feel secure enough to rest comfortably while still sharing the same bed. It can reflect both closeness and independence.
However, if the sleeping position changes suddenly along with tension or reduced affection, it may be worth talking about. In most cases, though, sleeping with your back to your partner is just a matter of comfort.
