Good neck posture means straight neck position. No sleeping with your head tilted or twisted to the side or forward. Think of how you would be positioned on a backboard after an accident. If you sleep on your side, your head should be supported so it does not drop to the side. If you sleep on your back, very little pillow support is needed under your head. Maybe some side support so your head does not roll to the side.

It take some getting used to to sleep on your back without a pillow lifting your head up. When you are asleep, there are no muscles to support your neck. Poor posture can put a strain on the ligaments supporting the cervical joints and cause inflammation.